Are you behind a firewall or do you have any antivirus enabled?
Try disabling anything that could block the Jabber's traffic, just for testing.
the problem with one or two users is calls in house, it worked before perfectly, the only thing that has changed is upgrade cisco jabber to version 12.1.
no problem with firwall because it works for other users
Try to check the routing between the 2 endpoints (Jabber and the other side).
If you know it, try to ping from the PC that you have Jabber the other end to check if you get a reply.