A few more details. The two computers using RO HQ are Win 7 64 bit, the one using RO standard is Win 7 32 bit. All dvd's are PAL stored on a NAS in Video_TS format.
Blu-ray stored in ISO and wts files recorded in wmc works as the should and resume the movie at the last point.
When I start a dvd it looks like for a second that it tries to resume, but then gives up and restarts the movie from the beginning.