It sometimes happens to me that I take a document from one machine, where it compiled without error, to another, where it produces a Too many math alphabets in version normal error. (Related: 1, 2, 3.) How can that be?
The two systems are quite similar (Ubuntu with TeX Live / Debian with TeX Live). There are no other errors, and the document seems to render correctly.
I have no MWE, but the document that prompted this question is a presentation made with beamer in arev. It includes the lines
\makeatletter
% get sans-serif \sum from Euler
\DeclareSymbolFont{EulerExtension}{U}{euex}{m}{n}
\DeclareMathSymbol\sum@\mathop{EulerExtension}{"50}
\makeatother
If I remove these lines, the error disappears. However, even with them I see no errors in the compiled PDF (I use pdflatex). Even the Euler sum sign is displayed as requested.
\listfilesto the source and edit in the two file lists this produces. – Joseph Wright Oct 04 '15 at 12:11