Conference Calls Drop after about 30 minutes

First just want to thank everyone in here who posts problems and more importantly the people who help answer them!!

I have 4 instances now where we had some conference call issues.

What has been happening:
External callers and internal callers call in to conference call and after about 30 minutes or so the call just ends.

I can account for 3 out of these 4 conference calls first hand.

I have traced calls with provider and the call drops point seem to point to the server/OS.

The funny thing is I have no issues with dropped calls for anything else.

Any input would be appreciated.