Views:

Behavior:
When opening the admin tool, you encounter an error message that reads: An item with the same key has already been added. The admin tool then closes. 
There is a key constraint violation between the DWUser and DWUserToGroup tables in the dwsystem database.

Solution:

IMPORTANT! Before beginning, make sure you have a backup of the dwsystem database!
Confirm that there are entries in the DWUserToGroup table that don’t have a corresponding UID in the DWUser table.

select UG.*
from DWUserToGroup UG left join DWUser U on UG.uid = U.uid
where U.uid is null

If this statement returns any results, a key constraint was violated when a user was deleted, and some records were left behind. To fix it, execute this query:
delete UG
from DWUserToGroup UG left join DWUser U on UG.uid = U.uid
where U.uid is null

You will be able to open the admin tool again.