Weirdly getting "! Argument of @tempa has an extra }" error in a really simple file

documentclass[journal=jacsat, manuscript=article]{achemso}

author{XX}
affiliation{Department of Physics,}

title[test]
{test}

usepackage{graphicx}

begin{document}


begin{figure}
includegraphics[scale=0.5]{example-image-a.png}
end{figure}


end{document}

This really simple latex file gives me the following error. I have tried changing the style of the document to article and the problem persists. I’ve googled the errors, and it doesn’t seem that I’m missing a "}" or "end{.}" statement anywhere. I’m really confused.

** Updated **

Any help is greatly appreciated.

This is pdfTeX, Version 3.14159265-2.6-1.40.19 (MiKTeX 2.9.6840) (preloaded format=pdflatex 2020.8.31)  1 SEP 2020 03:15
entering extended mode
**./test.tex
(test.tex
LaTeX2e <2020-02-02> patch level 5
L3 programming layer <2020-06-18>
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/ach
emso/achemso.cls"
Document Class: achemso 2020-05-27 v3.13a Submission to ACS journals

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/bas
e/article.cls"
Document Class: article 2019/12/20 v1.4l Standard LaTeX document class

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/bas
e/size12.clo"
File: size12.clo 2019/12/20 v1.4l Standard LaTeX file (size option)
)
c@part=count167
c@section=count168
c@subsection=count169
c@subsubsection=count170
c@paragraph=count171
c@subparagraph=count172
c@figure=count173
c@table=count174
abovecaptionskip=skip47
belowcaptionskip=skip48
bibindent=dimen134
)
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/xke
yval/xkeyval.sty"
Package: xkeyval 2014/12/03 v2.7a package option processing (HA)

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/generic/x
keyval/xkeyval.tex"
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/generic/x
keyval/xkvutils.tex"
XKV@toks=toks15
XKV@tempa@toks=toks16

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/generic/x
keyval/keyval.tex"))
XKV@depth=count175
File: xkeyval.tex 2014/12/03 v2.7a key=value parser (HA)
))
acs@bib@file=write3
c@bibnote=count176

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/geo
metry/geometry.sty"
Package: geometry 2020/01/02 v5.9 Page Geometry

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/generic/i
ftex/ifvtex.sty"
Package: ifvtex 2019/10/25 v1.7 ifvtex legacy package. Use iftex instead.

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/generic/i
ftex/iftex.sty"
Package: iftex 2020/03/06 v1.0d TeX engine tests
))
Gm@cnth=count177
Gm@cntv=count178
c@Gm@tempcnt=count179
Gm@bindingoffset=dimen135
Gm@wd@mp=dimen136
Gm@odd@mp=dimen137
Gm@even@mp=dimen138
Gm@layoutwidth=dimen139
Gm@layoutheight=dimen140
Gm@layouthoffset=dimen141
Gm@layoutvoffset=dimen142
Gm@dimlist=toks17

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/geo
metry/geometry.cfg"))
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/cap
tion/caption.sty"
Package: caption 2020/05/30 v3.4k Customizing captions (AR)

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/cap
tion/caption3.sty"
Package: caption3 2020/05/30 v1.12 caption3 kernel (AR)
Package caption3 Info: TeX engine: e-TeX on input line 61.
captionmargin=dimen143
captionmargin@=dimen144
captionwidth=dimen145
caption@tempdima=dimen146
caption@indent=dimen147
caption@parindent=dimen148
caption@hangindent=dimen149
Package caption Info: Standard document class detected.
)
c@caption@flags=count180
c@continuedfloat=count181
)
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/flo
at/float.sty"
Package: float 2001/11/08 v1.3d Float enhancements (AL)
c@float@type=count182
float@exts=toks18
float@box=box45
@float@everytoks=toks19
@floatcapt=box46
)
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/gra
phics/graphicx.sty"
Package: graphicx 2017/06/01 v1.1a Enhanced LaTeX Graphics (DPC,SPQR)

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/gra
phics/graphics.sty"
Package: graphics 2017/06/25 v1.2c Standard LaTeX Graphics (DPC,SPQR)

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/gra
phics/trig.sty"
Package: trig 2016/01/03 v1.10 sin cos tan (DPC)
)
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/gra
phics-cfg/graphics.cfg"
File: graphics.cfg 2016/06/04 v1.11 sample graphics configuration
)
Package graphics Info: Driver file: pdftex.def on input line 99.

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/gra
phics-def/pdftex.def"
File: pdftex.def 2018/01/08 v1.0l Graphics/color driver for pdftex
))
Gin@req@height=dimen150
Gin@req@width=dimen151
)
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/set
space/setspace.sty"
Package: setspace 2011/12/19 v6.7a set line spacing
)
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/url
/url.sty"
Urlmuskip=muskip16
Package: url 2013/09/16  ver 3.4  Verb mode for urls, etc.
)
acs@author@cnt=count183
acs@affil@cnt=count184
acs@affil@alt@cnt=count185
acs@footnote@cnt=count186
acs@affil@marker@cnt=count187
acs@space@pre@title=skip49
acs@space@post@title=skip50
acs@space@post@author=skip51
acs@space@post@address=skip52
acs@space@post@email=skip53
acs@maketitle@width=skip54
@float@every@scheme=toks20
c@scheme=count188
@float@every@chart=toks21
c@chart=count189
@float@every@graph=toks22
c@graph=count190
@float@every@table=toks23
acs@collect@toks=toks24
acs@collect@empty@toks=toks25
acs@tocentry@height=skip55
acs@tocentry@width=skip56

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/ach
emso/achemso-jacsat.cfg"
File: achemso-jacsat.cfg 2020-05-27 v3.13a achemso configuration: J. Am. Chem. 
Soc.
)
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/nat
bib/natbib.sty"
Package: natbib 2010/09/13 8.31b (PWD, AO)
bibhang=skip57
bibsep=skip58
LaTeX Info: Redefining cite on input line 694.
c@NAT@ctr=count191
)
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/ach
emso/natmove.sty"
Package: natmove 2010/01/15 v1.1a Automatic citation moving with natbib
)
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/mci
teplus/mciteplus.sty"
Package: mciteplus 2013/09/13 v1.2 enhanced mcite
@mcitetmptoksA=toks26
@mcitetmpdima=dimen152
@mcitetmpdimb=dimen153
@mcitetmpcnta=count192
@mcitetmpcntb=count193
c@mcitebibitemcount=count194
c@mcitesubitemcount=count195

** mciteplus: Detected natbib.sty. Invoking hooks.
))
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/l3b
ackend/l3backend-pdfmode.def"
File: l3backend-pdfmode.def 2020-06-18 L3 backend support: PDF mode
l__kernel_color_stack_int=count196
l__pdf_internal_box=box47
) (test.aux)
openout1 = `test.aux'.

LaTeX Font Info:    Checking defaults for OML/cmm/m/it on input line 13.
LaTeX Font Info:    ... okay on input line 13.
LaTeX Font Info:    Checking defaults for OMS/cmsy/m/n on input line 13.
LaTeX Font Info:    ... okay on input line 13.
LaTeX Font Info:    Checking defaults for OT1/cmr/m/n on input line 13.
LaTeX Font Info:    ... okay on input line 13.
LaTeX Font Info:    Checking defaults for T1/cmr/m/n on input line 13.
LaTeX Font Info:    ... okay on input line 13.
LaTeX Font Info:    Checking defaults for TS1/cmr/m/n on input line 13.
LaTeX Font Info:    ... okay on input line 13.
LaTeX Font Info:    Checking defaults for OMX/cmex/m/n on input line 13.
LaTeX Font Info:    ... okay on input line 13.
LaTeX Font Info:    Checking defaults for U/cmr/m/n on input line 13.
LaTeX Font Info:    ... okay on input line 13.
openout3 = `acs-test.bib'.


*geometry* driver: auto-detecting
*geometry* detected driver: pdftex
*geometry* verbose mode - [ preamble ] result:
* driver: pdftex
* paper: <default>
* layout: <same size as paper>
* layoutoffset:(h,v)=(0.0pt,0.0pt)
* modes: 
* h-part:(L,W,R)=(72.2698pt, 469.75539pt, 72.2698pt)
* v-part:(T,H,B)=(72.2698pt, 650.43037pt, 72.2698pt)
* paperwidth=614.295pt
* paperheight=794.96999pt
* textwidth=469.75539pt
* textheight=650.43037pt
* oddsidemargin=-0.00018pt
* evensidemargin=-0.00018pt
* topmargin=-37.00018pt
* headheight=12.0pt
* headsep=25.0pt
* topskip=12.0pt
* footskip=30.0pt
* marginparwidth=44.0pt
* marginparsep=10.0pt
* columnsep=10.0pt
* skipfootins=10.8pt plus 4.0pt minus 2.0pt
* hoffset=0.0pt
* voffset=0.0pt
* mag=1000
* @twocolumnfalse
* @twosidefalse
* @mparswitchfalse
* @reversemarginfalse
* (1in=72.27pt=25.4mm, 1cm=28.453pt)

Package caption Info: Begin AtBeginDocument code.
Package caption Info: float package is loaded.
Package caption Info: End AtBeginDocument code.

("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/context/b
ase/mkii/supp-pdf.mkii"
[Loading MPS to PDF converter (version 2006.09.02).]
scratchcounter=count197
scratchdimen=dimen154
scratchbox=box48
nofMPsegments=count198
nofMParguments=count199
everyMPshowfont=toks27
MPscratchCnt=count266
MPscratchDim=dimen155
MPnumerator=count267
makeMPintoPDFobject=count268
everyMPtoPDFconversion=toks28
)
("/Users/swan.h/Library/Application Support/MiKTeX/texmfs/install/tex/latex/eps
topdf-pkg/epstopdf-base.sty"
Package: epstopdf-base 2020-01-24 v2.11 Base part for package epstopdf
Package epstopdf-base Info: Redefining graphics rule for `.eps' on input line 4
85.
)

Class achemso Warning: No e-mail given:
(achemso)              at lest one author must have a contact e-mail on input l
ine 13.

LaTeX Font Info:    External font `cmex10' loaded for size
(Font)              <12> on input line 13.
LaTeX Font Info:    External font `cmex10' loaded for size
(Font)              <8> on input line 13.
LaTeX Font Info:    External font `cmex10' loaded for size
(Font)              <6> on input line 13.
Runaway argument?
"example-image-a.png" edef Gin@ext {Gin@sepdefault filename@ext }ETC.
! Paragraph ended before @tempa was complete.
<to be read again> 
                   par 
l.19 
     
I suspect you've forgotten a `}', causing me to apply this
control sequence to too much text. How can we recover?
My plan is to forget the whole thing and hope for the best.


! LaTeX Error: begin{figure} on input line 16 ended by end{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.21 end{document}
                   
Your command was ignored.
Type  I <command> <return>  to replace it with another command,
or  <return>  to continue without it.

(test.aux)
! You can't use `end' in internal vertical mode.
enddocument ... endgroup deadcycles z@ @@end 
                                                  
l.21 end{document}
                   
Sorry, but I'm not programmed to handle this case;
I'll just pretend that you didn't ask for it.
If you're in the wrong mode, you might be able to
return to the right one by typing `I}' or `I$' or `Ipar'.


! LaTeX Error: begin{figure} on input line 16 ended by end{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.21 end{document}
                   
Your command was ignored.
Type  I <command> <return>  to replace it with another command,
or  <return>  to continue without it.

)
! Emergency stop.
<*> ./test.tex
              
*** (job aborted, no legal end found)

 
Here is how much of TeX's memory you used:
 4183 strings out of 482725
 68831 string characters out of 2946709
 302690 words of memory out of 3000000
 19931 multiletter control sequences out of 15000+200000
 537228 words of font info for 40 fonts, out of 3000000 for 9000
 0 hyphenation exceptions out of 8191
 63i,3n,100p,229b,282s stack positions out of 5000i,500n,10000p,200000b,50000s
!  ==> Fatal error occurred, no output PDF file produced!