If you try to delete sub keys under USBSTOR key it will throw “Cannot delete <Key Value>: Error while deleting key.” error. To fix this i.e. to delete the sub key entries you need to assign permission to your account.
Right click on USBSTOR key and add permission to your account as shown below.
Now try to delete the key values.
Note: USB information is also stored in %windir%\setupapi.log file (Xp), for vista and later %windir%\Inf\setupapi.app.log
Update: Also check for the same in these locations