Workaround
User could use <NetBIOS of Domain>\<username> instead of <username>@<NetBIOS of Domain> format to log in.
Example:
If the NetBIOS name is ACME, the user will not be able to log in with the credential "
[email protected]" to Windows, remote desktop or VIP Credential Provider if the domain is hosted by Active Directory 2003. However, the user will be able to log in with "ACME\John".
Note: Logging in with username "
[email protected]" is supported by Windows, remote desktop and VIP Credential Provider for domains hosted by Active Directory 2008 or later.