OneX Communicator - Session Error

[aliceguzman]

Hi,
We use Avaya One-X Communicator 6.2 in Computer Mode (H.323) and have been experiencing issues with several users when dialing outbound calls.
After dialing, the softphone shows unknown (where the dialed number should be) for an abnormal period of time (over 10 seconds, hearing dead air) and then it pops up the Call Session Error.

If you just ok the error the call eventually might go through, but all subsequent calls have the same issue unless the application is restarted.
Also, when in this state, if a call is already active and the user hangs up (CM trace shoes the call ended, no more audio) but the call stays visually active and the timer continues running.

Weirdly, when this starts happening, another 5-8 users report the same issue.

We've updated 1XC to latest patch version, erased softphone configurations, erased Windows user profiles, tested with different station numbers and sometimes it appears to work, but after a few days it happens again.

Any ideas?