[USR-TC] Blocked channels in MultiSpan

Hi, I have a problem with a TC chasis ARC ver. 5.1.99 Multispan ver. 3.0.114, the problem is that each day i found blocked channels (max. 20- 30) when a user try to connect to the chasis PBX that redirect to call to the 6 E1 in 2 Multispan, the user listen the tone busy from the chasis, but when i see in the chassis i found that some channels are free but blocked... How i can solved this problem? How i can see alarms when a channels is blocked? the only way to unblock the channels is calling to Telco Company and they block out the channels.. thanks for your help... Wilder Tafur