Nope, never seen that message before.
Not very informative is it??
Are you given a chanse to resolve the missing file?
Try to pinpoint the problemfile by opening subassys and single parts.
If you cant pinpoint the problem, you can
1: wait for SP1 (appr 15 nov) and see if this solves it.
2: restore the 5.3-files from backup and work in 5.3, or try to migrate it again.