asterisk users - Feb 2009 - slip r errors nortel switch

I am connected with 5ess to a nortel switch. Running dahdi 2.1.04 and 
libpri 1.4.7 and asterisk 1.4.22
Everything is working for a short time.
The other side reports back to me that he is getting slip-r errors from 
the TE122P card.
After to many errors (like 11) the d channel shuts down on their side.

Any idea what to do about this?
I have not ran into it before.

Jerry