Pesky Login calling the wrong details?

Lets start with the “Log in” key

ConfigurationMode (0=Automatic, 1=Manual)
ServerAddressInternal (Internal Server Name for Log in)
ServerAddressExternal (External Server Name for Log in)
ServerSipUri (user Sign-in Address)
ServerUsername (domain username usually domain\user)

About this Key
It is automatically created when a user Logs in to AD. If it already exists then it is NOT over written by the login process.

Log in to OCS with Lync Client
reg add HKCU\Software\Policies\Microsoft\Communicator /v DisableServerCheck /t REG_DWORD /d 1 /f