This question is related to the answer to the question Is there a LaTeX trick to prevent a PDF viewer from copying the line number?
Unless you turn hyperref off, the following MWE
\documentclass{article}
\usepackage{listings}
\usepackage{accsupp}
\renewcommand*{\thelstnumber}{\protect\BeginAccSupp{ActualText={}}\arabic{lstnumber}\protect\EndAccSupp{}}
\lstset
{
language={[LaTeX]TeX},
numbers=left,
columns=flexible,
}
\usepackage{hyperref}
\begin{document}
\begin{lstlisting}
Hello\\
Universe!
\end{lstlisting}
\end{document}
cannot be compiled with the following error message:

How do I prevent conflicts between accsupp and hyperref?
\emptyaccsuppor to the key:numberstyle=\color{red}\tiny\emptyaccsupp. (Be aware that only the last command can take an argument! The other commands must be switches). – Ulrike Fischer May 24 '12 at 09:06