If the username is part of a sub-domain and contains an '@' symbol it was not possible to login to TM1 Ops Console.
The @ symbol was not in the valid list of accepted characters for login name
Resolving the problem
Ensure that the @ symbol is in the Userscreen.jsp file is deleted from the following lines :
<input dojoType='dijit.form.ValidationTextBox' id='username' regExp = '[^<>!~`#$%&*()^]+'