This is all I can find on it. You may need to contact NTAC to get more on it.
The command ISMC uses part of the System Message Alarm program to display ISDN trace information. Specifically it uses Minor Alarm messages. If the Minor Alarm System Messages have been disabled in System Data, then ISMC will not function. To enable Minor Alarm System Messages, set;
ASYD
SYS = 1
Index 91
Bit 2 = 0
Bit 3 = 0