I could fix the problem.
It occures every time when I automatically called an other form (it looks for updates and shows new releasenotes if an update was found) from within the OnActivate-Event of the main form where the SkinManager is located :wacko: .
After moving this “lookForUpdates”-call to OnShow-event of the main form all works fine 😀 .
Don't know why this is only a problem in WINDOWS 10, all works fine in WINDOWS 7 even if the call of the other form is in the OnActivate.
Regards
Siegbert