[Mapczar]

You are too low for the bomb to arm. Try skip bombing or better, a glide bombing pattern. Dive bombing take a lot of practice but is successful most of the time after some practice. Toss bombing in the least effective technique. although it can be mastered it is not historically accurate. No real combat pilot in his right mind would prefer such a risky and unreliable maneuver.

Also ... check you bomb delay. A minimum of 2.0 seconds or more is advisable when doing low altitude bombing.