我认为描述正在发生的事情的最好方式就是展示我看到这些错误的地方的一个例子。
\documentclass[12pt,letterpaper]{article}
\usepackage{fullpage}
\usepackage[top=2cm, bottom=4.5cm, left=2.5cm, right=2.5cm]{geometry}
\usepackage{amsmath,amsthm,amsfonts,amssymb,amscd}
\usepackage{lastpage}
\usepackage{enumerate}
\usepackage{fancyhdr}
\usepackage{mathrsfs}
\usepackage{xcolor}
\usepackage{graphicx}
\usepackage{listings}
\usepackage{hyperref}
\pagestyle{fancyplain}
\begin{document}
\section{Some section title}
Text
\subsection{Some subsection title}
Here is my paragraph about things, with a random inserted math thing $\frac{\pi}{3} \neq 1$. Then I start a new math thing
\[3>1\] % This is the line where I am getting an error
Here is more text. No error.
\end{document} % oddly there is an error here to, same one.