HiPath 4000 Users experiencing no dial tone but can still dial but then users have one way audio

[MAC_1992]

Users experiencing no dial tone but can still dial but then users have one way audio. This is a Hipath 4000 Version 3 software but with Version 1 hardware.
This is happening on all phones. You can pick the phone up 20 or 30 times you will have dial tone but on the 31st no dial tone. Very intermittent.
We have replaced power supplies, SIUX boards, switchover processors and the system runs ok for about a week but the problem comes back.
We have powered system off. The system seems to run for about a week then the problem comes back.
Verified grounding.

 

[masviss]

What messages are in the HISTA file?
How many LTU do you have? What type of LTU?
Do subscribers of all LTU have these problems?
Have you swapped LTUCE?