External program pdflatex finished with an error on lyx

3.6 with Miktex 20.11 (both x64 bits). I searched for updates of miktex.

My problem is that when compiling, exporting or previewing in pdf i got this error: external program pdflatex finished with an error.

I know there are more questions that talks about the same error but i’ve been trying to fix it for hours and i can’t solve it.

In the logs file says:

2020-12-10 12:38:14,118+0100 INFO pdflatex – this process (992) started by ‘cmd’ with command line: pdflatex archivo_nuevo1.tex
2020-12-10 12:38:14,134+0100 INFO pdflatex – allowing known shell commands
2020-12-10 12:38:14,134+0100 INFO pdflatex – enabling input (output) from (to) processes
2020-12-10 12:38:14,815+0100 FATAL pdflatex – Conversion from UTF-8 byte sequence to wide character string did not succeed.
2020-12-10 12:38:14,816+0100 INFO pdflatex – this process (992) finishes with exit code 1

Thank you.

P.S. Sorry for my english.