Hi folks,
Lately i had the same problem on a SP9100. By browsing all the posts about this problem (fly wheel loose, drum shaft connector ecc) and checking all these solution my problem was always the same. After changing boards, bias contact and all that stuff the problem was more simple than i thought. One of the inner contacts of the drum (B2469510) was bended inside and it was not touching the drum shaft all the time hence the error. Changing the drum was the solution.
Keep in mind if you see this error in field next time.