First time using Latex, I have searched the whole document for an extra { or a missing }, to no avail.
\documentclass[oneside,12pt,a4paper]{article}
\setlength{\parindent}{0mm}
\setlength{\oddsidemargin}{-5mm}
\setlength{\evensidemargin}{-5mm}
\setlength{\textwidth}{165mm}
\setlength{\textheight}{230mm}
\setlength{\topmargin}{-10mm}
\setlength{\marginparwidth}{15mm}
\setlength{\marginparsep}{7mm}
\usepackage{pslatex,palatino,avant,graphicx,color}
\usepackage[margin=2cm]{geometry}
\usepackage{hyperref}
\usepackage{amsmath}
\usepackage{indentfirst}
%\usepackage{gensymb}
\usepackage{setspace}
\doublespacing
\usepackage{graphicx}
\graphicspath{ {C:/Users/hill/Documents/Literature Review/Thesis_pictures/} }
\usepackage[english]{babel}
\usepackage[utf8x]{inputenc}
\usepackage{amsmath}
\usepackage{graphicx}
\begin{document}
\begin{titlepage}
\newcommand{\HRule}{\rule{\linewidth}{0.5mm}}
%----------------------------------------------------------------------------------------
% HEADING SECTIONS
%----------------------------------------------------------------------------------------
\textsc{\LARGE A Literature Review;}\\[1.5cm] % Name of your university/college
%----------------------------------------------------------------------------------------
% TITLE SECTION
%----------------------------------------------------------------------------------------
\HRule \\[0.4cm]
{ \huge {\color {blue}\bfseries Enhancing the efficiency of RF sources for future colliders}\\[0.4cm] % Title of your document
\HRule \\[1.5cm]
%----------------------------------------------------------------------------------------
% AUTHOR SECTION
%----------------------------------------------------------------------------------------
\begin{minipage}{0.4\textwidth}
\begin{flushleft} \large
\emph{Author:}\\
Victoria \textsc{Hill} % Your name
\end{flushleft}
\end{minipage}
~
\begin{minipage}{0.4\textwidth}
\begin{flushright} \large
\emph{Supervisor:} \\
Dr. Chris \textsc{Lingwood} % Supervisor's Name
\end{flushright}
\end{minipage}\\[2cm]
%----------------------------------------------------------------------------------------
% DATE SECTION
%----------------------------------------------------------------------------------------
{\large \today}\\[2cm]
%----------------------------------------------------------------------------------------
% LOGO SECTION
%----------------------------------------------------------------------------------------
\begin{figure}[fragile]
\setbox0\hbox{%
\includegraphics[width=0.45\textwidth]{UniLogo.jpg}%
}%
\setbox2\hbox{%
\includegraphics[width=0.45\textwidth]{STFCLogo.jpg}%
}%
\ifdim\ht0>\ht2
\setbox0\hbox{%
\includegraphics[height=\ht2]{UniLogo.jpg}%
}%
\else
\setbox2\hbox{%
\includegraphics[height=\ht0]{STFLogo.jpg}%
}%
\fi
\noindent
\end{figure}[fragile]
%----------------------------------------------------------------------------------------
\end{titlepage}
\clearpage
\tableofcontents
\clearpage
\section{Introduction}
\label{Intro}
\clearpage
%\chapter{Literature Review}
\begin{thebibliography}{20}
\bibitem{One}
First reference.
\end{thebibliography}
\end{document}
}
at the end of the document: it should highlight the innermost (last) unclosed{
.