The car has a factory alarm/imobliser that registers if the wheels rotate while the alarm is armed. Towing will do that. The system will imobilise the car until the alarm is reset. Might be your problem.
Good - Fast - Cheap: Pick any two.
E23 735i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i