Error Latex TeX capacity exceeded, sorry [input stack size=5000]

I get the same error with MikTeX 2.9, WinEdt 7 on Win 7. There is an undefined char (german umlaut?) in the pdfauthor property. If you remove/replace this character LaTeX runs until the \newtheorem{example}{Example} definition. Here one get the error that \example is already defined. Rename it and LaTeX compiles the whole document.

I'm getting Error Latex TeX capacity exceeded, sorry [input stack size=5000] in a beamer document when I try to make a block without a title and starting with an itemize environment:

This fails:

\begin{frame}{About Foo}
    \begin{block}   
        \begin{itemize}
            \item foo
        \end{itemize}
    \end{block}
\end{frame}

This works:

\begin{frame}{About Foo}
    \begin{block}{}
        \begin{itemize}
            \item foo
        \end{itemize}
    \end{block}
\end{frame}

Note the extra {} after the \begin{block}.

I had this happen and the problem was a statement like this:

\newcommand{\textyen}{¥}

Internally, somewhere else, the yen symbol was being mapped to \textyen. That of course made an endless loop

(gripe-on)The lack of a good error message that includes the exact symbol that it was processing at the time, or the exact line number of the file that it found it in, makes these problems many times more difficult to find/solve than they should be.(gripe-off)