Example to replicate the error message:
\documentclass{scrlttr2} \usepackage{rotating} \begin{document} \begin{sidewaystable} %\begin{tabular}{l} %test \\ %\end{tabular} \end{sidewaystable} \end{document}
\documentclass{scrlttr2} \usepackage{rotating} \begin{document} \begin{sidewaystable} %\begin{tabular}{l} %test \\ %\end{tabular} \end{sidewaystable} \end{document}