I work for a non-profit and I'm a Toshiba DIY'er and had the same issue when trying to install and configure a CIX100 with PRI for the first time.

Under:
System
System Data
Field 21 (Primary Clock) put the slot of your PRI card. For example mine is 010301

Hopefully this will fix you up.

I came here to post about a PRI problem our MD office is having. They have DK424 + RPTU + Contact DK and when people hang up in the middle of a message on the Contact DK it doesn't hang up and has a busy signal for the remanded of the allotted time for the message but if you press (any key when you're finished) it hangs up just fine. Our VM card gets full every 3 days now.