Seeing this error on a lot of our 300-19 CPE's when talking to a 2000 AP. Good SNR in all the cases, in one case swapping the CPE with another 300-19 resolved the problem for the time being but otherwise swapping them to a force-190 fixes it in all situations.
Possibly unrelated but we are also seeing the error "NO ALLOCATION ON AP" on some CPE's when connecting to the tower. The few we've seen in that situation were attached to a 2000ap that was upgraded with a key, and had been working fine.
All AP's and cpes are currently on 4.4.1 RC 5 - the ones we were having problems with were upgraded to 4.4.1 but it didn't fix any problems.