This applies to Recovery Solution 6.2 SP4, 7.0.x and 7.1 only. For all previous 6.2 builds please refer to HOWTO5697.
By default the 'Delete All User Data' task will delete your RS Client registrations in the RS SQL database as well. In order to delete user data while leaving Client registrations intact, the task should be performed manually using SQL Management Studio and by running following statement against your RS Database:
exec PurgeDatabase 1,1,1,1,1,0,0
This will delete all users backed up data, but keep their registration in tact.