After installing MiKTeX 2.9.6361 I tried to update all packages from CTAN (standard procedure from inside a script which sets up some other software which utilizes LaTeX). mpm --admin --verbose --update-db loaded miktex-zzdb2 and miktex-zzdb1 and apparently worked well, but the subsequent mpm --admin --verbose --update ruined my installation: I can no longer run pdflatex. If I try, I get a Windows popup, telling me that
The procedure entry point ?GetWrite18Mode@TeXApp@TeXAndFriends@MiKTeX@@QBE?AW4Write18Mode@123@XZ could not be located in the dll pdflatex.exe. I wonder why the exe is reported to be a DLL. But more I wonder what happened. Prior to calling mpm --update everything was allright.
The mpm update told me that 107 packages were going to be updated. It unregistered MiKTeX DLLs MiKTeX209-core-PS.dll, MiKTeX209-core.dll, MiKTeX209-packagemanager-PS.dll, MiKTeX209-packagemanager.dll (fishy?), downloaded and extracted several packages (probably 107) and re-registered the MiKTeX DLLs. No error message, no indication that anything failed.
Any advice? Current workaround is to deinstall and reinstall MiKTeX and not perform the update. Solutions found at SE (e.g. here) did not help.
Update
Using the basic 64bit installer 6520 everything worked as expected.
initexmf --admin --mklinks. – Ulrike Fischer Jan 08 '18 at 14:23