When a user has a large number of PST files assigned to their account, usually in the many thousands, you cannot reset the user in the PST Flight Deck Admin Console, and this error is returned:
The reset functionality was not designed to work when users have huge amounts of PST files assigned to them. You need to use SQL to reset the user.
You can reset the user by executing the attached SQL script against to the PSTFlightDeckDirectory database. You can download the SQL query here.
However, you need to update the script.
First, specify the ID of the user you want to reset. To find the UserEntryId value you need to right-click on the info bar in the FD Admin console and select Column Chooser as on following screenshot:
Double-click on UserEntryId column and it appears between the others in bar. This value represents the unique ID of the user.
Now you can edit provided SQL query by replacing the XXXX for the desired ID of the user in the 8th line of the code.
After running this script the the Reset User command is now complete.