No voice in SIP calls in LAN , no errors, no warnings

I have a problem, everything seems to be working fine but , i have no sound. I can hear Voicemail menu and messages that i have left to the accounts , but i cannot talk or hear during a call.

This is what i get when makking a call
– Executing [6004@numberplan-custom-1:1] Dial(“SIP/6000-08fd86f0”, “SIP/6004”) in new stack
– Called 6004
– SIP/6004-08fdbfe8 is ringing
– SIP/6004-08fdbfe8 answered SIP/6000-08fd86f0
– Packet2Packet bridging SIP/6000-08fd86f0 and SIP/6004-08fdbfe8
== Spawn extension (numberplan-custom-1, 6004, 1) exited non-zero on ‘SIP/6000-08fd86f0’

I have created users from GUI which are created in file users.conf
and i have added this lines in extensions.conf

exten => 6000,1,Dial(SIP/6000)
exten => 6003,1,Dial(SIP/6003)
exten => 6004,1,Dial(SIP/6004)
exten => 1001,1,VoiceMailMain

the thing is that before adding that in extentions.conf i got an error no IAX something , which was solved , but the very strange thing is that now at USERS GUI page i have the users i have created and i have also greyed out the users i have added. I cannot edit them from GUI.
Voicemail works fine.

Any help?

Thank you in advance.