asterisk users - Feb 2007 - 7912 issues half audio

I have a 6 - 7912's.
I have a TDM2402E echo cancel card.
Asterisk 1.2.12.1

Some times extension to extension the audio is only heard one way.
Some times extension to TDM2402 calls audio is only heard one way.

I have turned off the echo suppression on the 7912's config.

Any idea why it would be doing this?
Something to try?

THanks,
Jerry