you have to unassign the drive, start the array, stop the array, re-assign the drive, start the array.
This is needed to get unRAID to "forget" the drive that was in slot10. By re-assigning it, it makes unRAID think you've installed a new drive and it rebuilds the contents onto that drive.
I would run your old drive over a few preclears (once disk10 is rebuilt) to see if its still good, then re-add it to the array.
If this is true, make sure to mark that original slot as defective so you don't use it in the future.