CommonControls (Replacement of the MS common controls)

[Krool]

And this makes trouble.
If I set Cancel to true, then I can't select a tab at all.
I could manage the Cancel value, but I think this is not a good approach.

When you select the Tab during MouseUp you Need to flag an private variable (form variable) so during that selection you do not set Cancel to True in the TabBeforeClick Event.
I think the event will also be fired when you Change the tab by code. So in that exception you need to by-pass it once.