I might be talking rubbish since I haven't fitted a roof/motor but is it possible that the roof or micro switches need adjusting? This must be worth eliminating first as the overfilled fluid idea sounds less likely.
http://tis.spaghetticoder.org/e85/Z4_3.0i_%28M54%29_ROADST/Slide-tilt_sunroof_and_convertible_top/convertible_top_linkage-operation/