Recurring outbound GPRS Attach Accept messages

All, Apologies if this is the wrong mailing list for this question. If so, please redirect me to the appropriate Osmocom list. Thanks! I'm having trouble with some older 2G cellular modules. When they initiate GPRS, the GPRS Attach Accept response from the SGSN seems to be dropped on the floor. I thought this was because the inbound TLLI generated by the ME was not included in the subsequent response. However, I verified that the LLC correctly generates the response and attaches the TLLI. I'm not quite sure why these particular 2G modules are not receiving the response as the message seems to be correctly submitted from the SGSN to the BTS. The result is that the GPRS state will get "stuck" on the ME side, which will keep attempting to Attach until it gives up and issues a Detach message (under the same TLLI). Can anyone clue me in on what potential issues may be caused by this ME and how/if I can patch this problem in the SGSN? Thank you, D