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Marian's worked on my laptop but not on my desktop.

on my desktop, I had to solve the problem THIS way.

As Administrator, uninstalled miktex and texmaker.

Reinstalled miktex to a fresh directory, reinstalled texmaker next.

Did as Marian advised, Build , Update FMT, Update FNDB.

Then it works.

Yes, Marian's solution (<Build format> files, then <update formats> + <Update FNDB> in MikTex 2.9 as Administrator) works. That solution should be marked as a email to read before posting anything else.