Can´t make calls (out inv)


I’ve ben havin a problem with my pbx configuration

I’ve set up 2 cisco 7960 with SIP and both get the configuration from the server both register.

now the problem is

on phone 1 ext. 1001 i can recieve and call phone 2 ext 1002.
but on phone 2 ext 1002 i cant call phone only receive 1 ext. 1001

so on end point manager i switched the extentions to see what would happen.

phone 1 ext 1002 can only recieve calls when it makes a call i get the out inv message

phone 2 ext 1001 can now make and recieve calls.

iv checked the files and they are right.

i’ve had this 2 phones set up at home and running perfectl but now at my work place i can not do it.

any help ?