User has a 924, with a DID trunk on FXO ports. Lines are used for inbound only, no outbound calls at all.
Approximately 20% of inbound calls fail, and the debug shows "glare", but since there are no outbound calls, both sides should not be seized at the same time.
His PBX is expecting wink start, which isn't an option from the Adtran on an FXO port, so we use DPT.
Is there another reason calls fail with with "glare" error?
Probably because the PBX is expecting a wink. Can you option both the PBX and the TA900 for ground-start? This should virtually eliminate glare. You'll need to ensure that they share a common ground and that polarity is correct.