[USR-TC] Cannot logon to TC1000

I have a TC1000 with ARC 5.3.3/non-encr software. I have configured the card to use chap. Here is my problem. I can use a Cisco 1700 router to logon to the TC, I can use Windows to dial into the TC, but when I try to use a Nortel ARN to logon, I get a chap failure mismatch. I have another TC1000 with V4.1.11 that all can dial into without problems. I have tried to duplicate the configuration, but I must be missing something. Any suggestions? Thanks -Jim