Please help with VOIP Problem

[Coldfuzion]

I have a very odd issue going on with a small VOIP setup. I have a new 5gt and a ns50, with a vpn setup between the two. They are both running os 5.3. I have a couple of VOIP phones setup in the smaller ofice (with the 5gt), and am getting a very strange dial tone problem.
When picking up the handset, it will take 4 or 5 times (of picking up, then hanging up, etc....) before dialtone is achieved. when this happens, i see in my netscreen logs this notif:

notif NetScreen devices do not support multiple IP addresses 1 or ports -1062731611 in SIP headers RESPONSE
notif NetScreen devices do not support multiple IP addresses 1 or ports -1062731611 in SIP headers RESPONSE
notif NetScreen devices do not support multiple IP addresses 1 or ports -1062731611 in SIP headers RESPONSE
notif NetScreen devices do not support multiple IP addresses 1 or ports -1062731611 in SIP headers RESPONSE
notif NetScreen devices do not support multiple IP addresses 1 or ports -1062731611 in SIP headers RESPONSE
notif NetScreen devices do not support multiple IP addresses 1 or ports -1062731611 in SIP headers RESPONSE

Now on the phone itself, there is a second line button, if i press that button, then pickup the handset, i get dialtone immediatly. I also see this notif in my netscreen logs:

notif NetScreen devices do not support multiple IP addresses 0 or ports -1062731611 in SIP headers INVITE
notif NetScreen devices do not support multiple IP addresses 0 or ports -1062731611 in SIP headers INVITE

Does anyone have any idea what is causing this and how i can fix it?

Thanks in advance.