I have 2 users out of 400 that when they log into their presence client they can't come out of "invisible" status. Everything looks correct in the settings in UCM and the Presence server. All users are configured the same. What could possibly cause this?
Normally when you try to set the presence status on the client, it should communicate with CUP server and then the CUP server will send a SIP publish message to the CUPC with the new presence information.
I am guessing that your two clients are not getting that message.
You can put a sniffer and test it with a working scenario (just to see what kind of sip messages you should be expecting to see) and then check it out with those two clients.
There must be an issue with the commincation between the client and the server.
Of course if there is anything block something ie firewall (especially on the clients PC) it might be a good idea testing without it.
once we find where the communications fails we investigate further.