Hi Colm,
Did you place the krb5.ini and the bscLogin.conf in the respective directory on the client. You may also need to add this to the lumiradesktop.ini file
-Djava.security.auth.login.config=<Location of bscLogin.conf>\bscLogin.conf
-Djava.security.krb5.conf=<Location of Kerberos>\krb5.ini
Also on the BI Platform, configure the properties of the WACS services to include the path to both of the above files (i presume you would have already kept the file since SSO is already configured)
Let me know if this works
Regards