\documentclass{article}

\providecommand{\tabularnewline}{\\}

\begin{document}

\section{Dummy}

If I remove this section (the first one), then the table works.


\section{Chapter 2: The table}

Here comes the table, a normal one:

\begin{tabular}{|c|c|c|}
\hline 
Header1&
Header2&
Header3\tabularnewline
\hline 
A1&
A2&
A3\tabularnewline
\hline 
B1&
B2&
B3\tabularnewline
\hline 
C1&
C2&
C3\tabularnewline
\hline
\end{tabular}

Here finishes the table
\end{document}
