I spent a few hours in IRC #mediaportal channel with user rolfey. We fixed the same issue with a deep cleanup using this script: https://forum.team-mediaportal.com/improvement-suggestions-46/full-directory-cleanup-during-uninstall-31291/. Works fine in both XP and Vista.
Simone
I could solve the issue by adding the missing entries to the SQL database like gibman said. Thanks anyway!
nachttier