LaTeX.org

Thanks for your prompt reply. As far as I can tell, the problem turned out to be a corrupted MikTex installation. My MikTex Updater runs persistently failed for several days in a row a few weeks ago, and I suspect that left some packages in a corrupt state. I did a fresh install of MikTex, and the ...

I have recently (since a Miktex auto-update in late June 2011) seen a problem in siunitx.
Minimal working example is:
\documentclass{article}
\usepackage{siunitx}

\begin{document}

stuff

\end{document}

and the logged error is
\..\Application Data\MiKTeX\2.9\tex\latex\siunitx\siunitx.sty(805 ...