I have this problem with ISDN2e lines coming in to a 1760 and onto a CCM3.3. Occassionally when you dial the main number you get engaged tone (even though there are lines available) and the debug isdn q931 shows a temporary failure with a code of 1x80A9.
I have replaced the router and all the BRI cards but the problem persists. I'm convinced that this is an exchange fault but BT deny it.
Has anyone come across this before and have any tips?