DoS error with Netgear DG834 ADSL router

[voipnow]

I get the following entry in the modems log
UDP Packet - Source:82.53.124.207,1538 Destination:165.165.208.233,3050 - [DOS]

This is exactly when making a voip call

How do i prevent the modem from seeing the incoming packets as a DoS attack.

Any help please
Steve