Looks similar to a problem I raised a TAC case for.
You need to raise a case with Cisco WebEx team and find out if your org (e.g. company.com) is associated through CUP or WebEx. If you want to federate through CUP then you need to remove it from WebEx connect's Org admin, apparently they are mutually exclusive. Sort of makes sense in that if you run WebEx connect clients why run Jabber clients? Can be a problem from admin POV if you actually use WebEx connect, so be careful:
1. ALL Connect accounts must be deactivated in orgadmin.
2. All accounts and buddy lists will be lost forever once the domain is removed from WebEx.
- if you use WebEx and the WebEx Connect association is an admin error then it is no big problem to remove it as it should not make a difference.
I spent ages troubleshooting my "XMPP error" before I found out the problem. Hope that this helps you.