[USR-TC] D-Channel Down on HiperDSP Multispan (on second/third spans)

hi, i am experiencing the following problem. - in a HiperDSP Multispan nic when i use the first span the d-channel comes up nicely and i am able to connect and surf... but whenever, i try to swing the same line from first span to second/thrid span on the nic the nac always have a d-channel alarm.. and gives me fast busy tone on dialin. any suggestions/ideas would be more then welcome. rgds,