I use combination of inputenc package (originally using 'latin2' encoding, but using 'utf8' encoding gives the same error) and fontenc package with T1 font encoding for writing LaTeX.
This combination gives strange bug when using 'Ł' or 'ł' (lslash) inside fragile frame.
Example code:
\documentclass{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\begin{document}
\begin{frame}
\frametitle{Non-fragile frame}
Łł
\end{frame}
\begin{frame}[fragile]
\frametitle{Fragile frame}
Łł
\end{frame}
\end{document}
Compiling this document with LaTeX or PDFLaTeX gives the following error:
[1] (./beamer-test.vrb
! Undefined control sequence.
l.2 \T
1\L \T1\l
?
Replacing ł with \l (or {\l}, or \l{}) generates correct output without any errors. In original 'latin2' (iso-8859-2) 8bit encoding there were no problems with any other Polish character, only with ł.
tetex-3.0-9.FC4
pdfeTeX 3.141592-1.21a-2.2 (Web2C 7.5.4)
beamer 3.01
fontenc 2004/02/22 v1.99f
inputenc 2004/02/05 v1.0d
beamer. – Herbert Nov 19 '11 at 13:07beamerrequires installingpgfcore... – Jakub Narębski Nov 19 '11 at 13:13beamer(and installingpgf), or rather installing it locally to~/texmffixed the issue. Thanks. – Jakub Narębski Nov 19 '11 at 15:06