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Missing ddl

i upgraded to windows 10 now i get this error (UE4Editor-WindowsMoviePlayer.ddl) asking if i want to rebuild it.

Have you tried to re-download the .github binaries? After that, try to validate file caches of the devkit… HOPEFULLY that fixes your situation. It is entirely possible that windows 10 integration into this custom version of UE4 is not compatible though.