Please do a defrag, if possible. I've had strange errors myself that went away when I had the defragger runnung - especially concerning heavily fragmented (big) files.

There should still be a free version of "O&O Defrag" be in the depths of the internet; O&O is a German company which made a fairly well impression to me.
Alternatively, you could use the defrag program of the German magazine c't , which you can find here : http://www.heise.de/ct/ftp/ and to be exact here : ftp://ftp.heise.de/pub/ct/ctsi/hdtool11.zip
These two defrag programs are seeminly for NTFS only. Sorry, for FAT users (like myself).

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