asterisk users - Mar 2005 - Broadvoice busy message every couple of days.

I have my broadvoice asterisk server up and running.  For some reason 
after every couple of days you call the number and it says the number 
you are trying to reach is busy and cannot take your call right now.

I then stop asterisk and start it and it is fine for a couple days.

Has anyone else had this issue?  Any idea why?

Randy