PRI b-channel LCKO problem between Cisco VOIP Gateway and Nortel 61C

Hi, I have a PRI between a Nortel 61c and a Cisco VOIP phone system. It allows us to 4-digit dial between the two phone systems. The PRI terminates into a 6608 gateway blade in our 6509 chassis system on one end and a PRI card in the Nortel (loop2) on the other. Every couple of months, I would have to disable and re-enable Loop 2 because the b-channels get locked out. Finding out why the channels go LCKO was not a big issue at the time because it didn't happen any more often than the b-channels on two other PRI's. We recently deployed 7 Cisco VOIP wireless phones in a manufacturing area with two Cisco access points and now I have to disable and re-enable Loop 2 every other day. I noticed on my Nortel terminal one morning an error referencing the loop and the channel and reason 44. Does anyone know what causes b-channels to LCKO? Does anyone else have any experience with this type of problem?? Thanks in advance. CAsniffer