asterisk users - Mar 2008 - Broken calls during conversation

Good morning,

we face a problem with Atserisk 1.4.18.1 and Zaptel 1.4.9.2: calls are 
frequently ended during conversation or voicemail are not registring the 
entire messages given by callers.

What we have -and seem strange- is:

Module                  Size  Used by
ztdummy                10312  0
zaptel                200264  11 ztdummy ;<- THIS
crc_ccitt               6784  1 zaptel

We have various phones brand (Snom, Polycom, Tiger) and they all have 
this behavior.
The server is a Dell SC440 without any telephone card, Debian ETCH. 
ztdummy is used for meetme and voicemail application only.

Another strange think in logs

[Mar 31 10:15:19] VERBOSE[8370] logger.c: RTCP SR transmission error, 
rtcp halted

Thanks for any hint.

-- 
Daniel
TOOTAi Networks