HTTP Status 500 error on login

HTTP Status 500 error on login


I am getting a Tomcat error on login to ServiceDesk Plus (see attached screen shot).
 
I've tried logging the issue online but have had no response.
 
I've seen this mentioned on the forums a few times but no solution is posted, has anyone fixed this before ?
 
It's a real problem as it's locked out myself (the only system admin) and our front line helpdesk person.

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