I have had this before when trying to create a rotating cog.
All I did (probably the slowest way to achieve the same result) is added a keyframe for EVERY step of the rotation.
So, I started off with no keyframes, hit 'I' to insert a keyframe, then press 'R' to rotate, then while holding Ctrl, move the model ever so slightly until it rotates round one 'click', then let go, hit 'I' and insert a new keyframe. I did this for every click until my model had completed a full loop and it animated perfectly inside FPSC.
As I said, there is probably a much easier way to do this, but, I didn't know at the time. This is quite a rough and dirty fix, but, it works.
Jay.