On a few occasions, I have experienced either one way audio, or no audio on PRI with CIX100 and CIX670. I believe this is caused by a momentary outage from the carrier, and for some reason the D channel renegotiates, but the B channels do not carry audio.
Usually a reset of the PRI card as phonemeister suggested has cleared my issues, however I did have another issue the other day (CIX 100 running 3.1 MK043): the customer could hear just fine, until they would build a conference call with 2 outside callers. When this was done, they would see on the display "CHG 1 + CHG 1", and the two remote parties could hear each other, but neither could communicate with the Toshiba user who built the conf call. A reset of the PRI card did NOT clear the issue, however a reboot of the system did.
Hope this helps,
Sam
