SPA504G : Incoming calls are dead when picked up.

[voiptelephony]

i have an issue with my voip system. it does not allow me to answer incoming calls .the phone is ringing but when pick it up it's dead. at the moment i have a  Netgear router , ports 5060 and 10000-20000 are open .

there are few thing i did so far like turning off SIP ALG on the router and also reducing expiry time to 2 minutes ,but to no avail .

i also did following setting as NAT setting 

Nat mapping enable:yes

keep NAT aliv enable:yes

Handle VIA received:yes

Insert VIA received:yes

Handle VIA rport:yes

Insert VIA rport:yes

Send Resp to Src port:yes

any thing else i can do to solve this out ?

Thanks,

[Dan Lukes]

Capture SIP packets and syslog/debug messages related to incomming call

Then we can analyze the problem.