Moderncv theorem environment error

I am using the following research statement template. In my statement, I have to use the environment of the theorem, lemma, definition. It is giving me error when I am compiling my LaTeX file. I could not find the error. Any help appreciated.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% "ModernCV" CV and Cover Letter
% LaTeX Template
% Version 1.1 (9/12/12)
%
% This template has been downloaded from:
% http://www.LaTeXTemplates.com
%
% Original author:
% Xavier Danaux ([email protected])
%
% License:
% CC BY-NC-SA 3.0 (http://creativecommons.org/licenses/by-nc-sa/3.0/)
%
% Important note:
% This template requires the moderncv.cls and .sty files to be in the same
% directory as this .tex file. These files provide the resume style and themes
% used for structuring the document.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%----------------------------------------------------------------------------------------
%   PACKAGES AND OTHER DOCUMENT CONFIGURATIONS
%----------------------------------------------------------------------------------------

documentclass[11pt,a4paper,sans]{moderncv} % Font sizes: 10, 11, or 12; paper sizes: a4paper, letterpaper, a5paper, legalpaper, executivepaper or landscape; font families: sans or roman

moderncvstyle{casual} % CV theme - options include: 'casual' (default), 'classic', 'oldstyle' and 'banking'
moderncvcolor{blue} % CV color - options include: 'blue' (default), 'orange', 'green', 'red', 'purple', 'grey' and 'black'

usepackage{lipsum} % Used for inserting dummy 'Lorem ipsum' text into the template

usepackage[scale=0.75]{geometry} % Reduce document margins
%setlength{hintscolumnwidth}{3cm} % Uncomment to change the width of the dates column
%setlength{makecvtitlenamewidth}{10cm} % For the 'classic' style, uncomment to adjust the width of the space allocated to your name

usepackage{amsfonts, amsthm}
usepackage{amsmath}
usepackage{amssymb}
usepackage{booktabs}
usepackage{color}
usepackage{colortbl}
usepackage{enumitem}
usepackage[utf8]{inputenc}
usepackage[english]{babel}
%usepackage[hang,flushmargin]{footmisc}
%usepackage[margin=25mm]{geometry}
%usepackage{mathtools}

newtheorem{theorem}{Theorem}[section]
newtheorem{corollary}{Corollary}[theorem]
newtheorem{lemma}[theorem]{Lemma}


%newtheorem{theorem}{Theorem}
%newtheorem{specialthm}{specialthm}
%renewcommand*{thespecialthm}{arabic{specialthm}}


%----------------------------------------------------------------------------------------
%   NAME AND CONTACT INFORMATION SECTION
%----------------------------------------------------------------------------------------

firstname{} % Your first name
familyname{} % Your last name

% All information in this block is optional, comment out any lines you don't need
%title{Research Statement}
%address{}{}
%mobile{()}
%phone{(000) 111 1112}
%fax{(000) 111 1113}
%email{}
%homepage{staff.org.edu/~jsmith}{staff.org.edu/$sim$jsmith} % The first argument is the url for the clickable link, the second argument is the url displayed in the template - this allows special characters to be displayed such as the tilde in this example
%extrainfo{additional information}
%photo[70pt][0.4pt]{pictures/picture} % The first bracket is the picture height, the second is the thickness of the frame around the picture (0pt for no frame)
%quote{"A witty and playful quotation" - John Smith}

%----------------------------------------------------------------------------------------

begin{document}
makecvtitle % Print the CV title
%----------------------------------------------------------------------------------------
%   EDUCATION SECTION
%----------------------------------------------------------------------------------------

section{Previous Research Experience}
begin{theorem}
Hello new
end{theorem}

begin{lemma}
end{lemma}

{hskip 2em}  


%----------------------------------------------------------------------------------------
section{Research Goals}





end{document}