Sorry, I just think it's funny. Currently supported releases of Plex, 6.0 and 6.1. Releases of Plex that support Windows 7. Plex 6.1.
Thisdocument should help you with compatibility.
Ok, moving on. When you say "every other application works fine" do you mean every other Plex Application, or something else. If it is every other Plex application, are the other Plex applications using Native or WinWidget controls?
Crispin.