fontspec-error

Dear MikTeX users,

Since two months (since the major-updates in November) I have the following
problem on two different Computers. I am using LuaLaLaTeX and fontspec and
i get at least 6 error-messages from fontenc.sty, fontspec-luatex.sty and
t3enc.def (see attached log-File), when I compile a file, starting with
this error:

Font \EU2/lmr/m/n/10=file:lmroman10-regular:script=latn;+trep;+tlig; at
10pt not loadable: metric data not found or bad.
\fontencoding\encodingdefault\selectfont

**** MWE.tex ****

\documentclass{scrartcl}

\usepackage{fontspec}

\begin{document}
Das ist ein Minimalbeispiel.
\end{document}


**** MWE.tex ****

I think I am missing something very obvious because I didn't find anything
on this in the archives. But the problem remained, even though i did a
complete reinstall of Windows 10 and MikTeX on one of the computers.

Thank you very much,
Martin

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