The following code used to compile with TeX Live 2014, but does not compile with TeX Live 2015. I now get the error:
! Missing \endgroup inserted.
<inserted text>
\endgroup
l.158 \closing{Yours Sincerely}
This may be related to changes in KOMA. None of the other relevant package appear to have changed recently. I'd be interested in an explanation of why this no longer works.
\documentclass[12pt]{scrlttr2}
\usepackage{mdframed}
\surroundwithmdframed[linewidth=2pt]{tabular}
\usepackage[T1]{fontenc}
\usepackage{fouriernc}
\begin{document}
\def\today{6th April, 2015}
\begin{letter}{Addressee}
\opening{Dear,}
\closing{Yours Sincerely}
\end{letter}
\end{document}
\closinguses a tabular internally while measuring the width of itself. Surrounding that with a frame leads to the error message you encounter as shown in chat already. – Johannes_B Dec 14 '15 at 10:30\surroundwithmdframed[linewidth=2pt]{tabular}. – Faheem Mitha Jun 10 '16 at 16:47