cannot generate sspi - None of Solution worked!
Having no SPN does not cause this error. Having an invalid SPN does. It's not enough to make sure an SPN exists, you have to make sure it is owned by the SQL Server service account and that it is configured correctly.

Follow the advice I blogged here: http://sqlsoldier.net/wp/sqlserver/advanced-troubleshooting-week-at-sql-university-lesson-1