Just found it out as I installed my mousesoftware.
When there is a mousesoftware running that defines middle and other buttons, it is inpossible to rotate anything in GalCivII. Even when I set the middle mouse button to the "middle mouse button" function (thats actualy no function at all), it does not work (logitech mouseware). Tried it out with a microsoft mouse and microsoft software, same result. Got to deinstall the software in order to play GalCivII... big deal to have a 5 button mouse where I can still use just 2 and installing deinstalling all the time is no option.
Suggestion: definable key bindings in GalCivII would resolve this