The following document doesnt't compile in miktex:
\documentclass[10pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[light]{merriweather}
\begin{document}
blub
\end{document}
Adding \pdfmapfile{=merriweather.map}
does not resolve the problem. The map file has been activated but the map-file itself is faulty: It contains only a few entries for LY1-encoding. The map-file on CTAN is much larger. Looking at the dates it seems that the package has been updated after miktex packaged it, so repackaging and updating the package will probably resolve the problem.