We have configured the VOIP service to work with our provider OnSip and are getting mixed results. For most of us the incoming and outgoing calls work great. However, we have a couple of users that the calls just don't seem to go through at all. We are seeing this in the log file:

POST /web/dataset/call_kw/voip.phonecall/rejected_call HTTP/1.0" 200

Can anyone help in telling us where to start on this. All credentials are fine, and system seems to authenticate fine, Other Users are working so it is not a module configuration user. All groups are the same and even privs elevation has no impact. Browsers are fine as we have checked working users across different machines and the others work.