It shouldn't be UCM down as that should still log you in and tell you it used the local emergency copy of the account details. Your CS1K is it Linux or VXWorks CS and when you say you can login with Root are you talking about the linux base as thats not an account normally associated with the callserver?
Needless to say what type of system is it, on what hardware and what you trying to access?
As admin2 is not normally in the UCM (unless you added it), if you can login to the CS with admin2 then it would point towards the CS not being in the security domain. If you are talking about the linux base of a server then I would normally use admin2 anyway but you could try re-registering it to the sec domain, check certificates in UCM/SMGR etc.