The chemmacros package contains beside others in the newest version "quite a number of module files following the naming scheme chemmacros.module.*.code.tex", e.g. http://mirrors.ctan.org/macros/latex/contrib/chemmacros/chemmacros.module.base.code.tex
All this module files are missing in the newest miktex update and so this document fails:
\documentclass{scrbook}
\usepackage{chemmacros}
\begin{document}
Text
\end{document}
This will be fixed with the next update.