[Serusers] Authentication problem.

I can call SER with a phone registered to it, no problem. When i try to make outbound calls to my provider, they fail with. 407 - proxy authentication required. I cant seem to trace it down: if (method=="REGISTER") { # Uncomment this if you want to use digest authentication if (!www_authorize("sr.mydomain.com", "subscriber")) { www_challenge("sr.mydomain", "0"); break; }; save("aliases"); save("location"); break; }; Is this a problem at my end or my providers? I am new to SER, is there something i am missing? Thanks.