problem isdn test call on 1841 device

Hello,

I'm trying to test an ISDN connection by an ISDN manual call, like this : isdn test call interface BRI 0/1/0 02xxxxxxx (x = remote isdn number)

and i have this message on my screen : ASSERTION FAILED: file "../chips/gt96k/gt96k_timer.c", line 771

My IOS version is : Version 12.3(8r)T8

thanks for your help

Regards

Arnaud