As a first troubleshoot method, resetting Jabber is likely to fix a lot of issues:
1. Open Jabber, and select the circle on the the top left of the screen, just above the little person.
2. Click sign out.
3. On the sign in page, click "Reset Jabber" just below the "Sign In" button.
4. Have the Caller read over the following and make sure this is fine, then click "Reset"
5. Have the Caller sign in again, then resolve or proceed with other troubleshooting options.