OS: Win7 x64bit SP1

OCS: 2007 R2

I have 3 OSC users account activated by my parent company.

I setup up the 1st user's laptop and signed in without a problem. and then I tested the other 2 users account on this 1st user's laptop as well. all working fine.

Problem: when i setup the other 2 users' laptop. OCS failed to sign in with msg "Cannot sign in - server temporarily unavailable".

I have no idea what went wrong. all 3 laptops have the same OS and SP configured. all 3 accounts work fine on the 1st user laptop but not on the other 2 laptops...

• Edited by Andrew.Lee Monday, April 11, 2011 8:01 AM

I found out that when OCS sign in, it uses SSO (which is your current windows Logon). and this will not work on my environment as the clients and servers are in 2 different domain.
So I have to disable the SSO so that OCS will prompt me with Custom Authentication(CA)

in order to do this, below are the steps:
1. run REGEDIT
2. goto HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft
3. Right Click on Microsoft and create a new Key named "Communicator"
4. in side the Communicator Key, create a DWORD
5. name the DWORD "DisableNTCredentials"
6. Change the DWORD value from 0 to 1

Relaunch the OCS and you will be direct to the authentication page straight away.

• Marked as answer by Andrew.Lee Monday, April 11, 2011 8:00 AM

I tried the many fixes to resolve this. I finally fixed it by deleting the SIP information and other cache:

1. Exit Communicator completely (right-click the icon on the system tray and choose EXIT)

2. Browse to the C:\Users\<user_name>\AppData\Local\Microsoft\Communicator

3. Delete the SIP_username@domain.com folder.

4. Start Communicator. The SIP folder will be recreated.