Before starting your scan/defrag make sure all running processes are stopped. Press ctrl/Alt/Delete then highlight a running process and press Stop (doing this from memory - think it says 'Stop' or similar) Do this to all running processes one at a time except Explorer ........ then try to scan/defrag again. When it says "something is writing to the drive" it is referring to these running programs which are normally invisible to you, until you press Ctrl/Alt/Del. During the scan/defrag do not touch your mouse.......just be patient!
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