External VRU fails to respond

NOTE: I was given erroneous information about version. I have confirmed: Asterisk 1.8.11-cert5

Our company has a simple VOIP phone system:
[ul]Cisco IP Phone 7940 Series (typical, some other models, too)
Asterisk server (v2.10.x)
Router/Cisco 2801
Phone Box/provider
VRU/IVR - totally outside our company (e.g., join somebody’s teleconference)
Sometimes when using one of our internal phones, typically to join a teleconference outside our company, our user is prompted by a voice menu and NO key press moves the VRU to next step.

The problem is intermittent, sporadic and has no test case where the problem always occurs.

There is no pattern/correlation to affected users, phones on which this occurs, time of day, external phone numbers nor external VRU.

Sometimes, hanging up on a hung connection and redialing resolves the problem; but, sometimes the problem persists across multiple calls in a short time span.

Please, advise. Thank you.

I’m surprised that I got no response at all from this post!

Not even a: “You idiot! You don’t have a clue …”

Clearly, the people on this forum know a lot about Asterisk and VOIP phone processes, and I know next to nothing.

Please, hit me with a clue stick!