one way calling only problem via analog card

Hello everybody.

first of all thank you for all the support you give us all the time. I (and I know for sure I not the only one) am really thankful to all of you.

let's talk problems now.
I have tb 2.6.1 on a PIV machine (the old PC :-)) and I have an Digium TDM400 card with 4 FXO modules. everything was working fine (for almost a year now) until recently when I encountered the following problem. When I dial through an analog trunk I hear nothing but echo. I have checked the CLI and the call seems to be established successfully but he other end does not ring (the call actually does not go through). on the other hand, if I dial into the PBX from outside everything works just fine.
I tried to update the modules via web but no solution to the problem. I even upgraded the entire PBX via yum. same result. I am thinking to recompile zaptel but, isn't that done when you do the update / upgrade???

have anybody had the same problem before?

thanks

Lorenc