Vista File Corruption

I have run into yet another problem with Vista. I've noticed a problem on a number of files now, at first the files are OK, I can open them and view them, but later when I try to open them I get an error message that just says can't open file. This is happening often. This happens to the file even if I make no changes to it. At first they are OK, then later they are not.
Although I get the same error message sometimes the file size stays the same, this time it changed to zero bytes.

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