XP defragmenter size limitations

A friend is having trouble defragmenting his C: drive, which includes a 14 gig file. The defragger completes with a note that it cannot defrag the file in question, which is a container file for a virtual drive.

I can't find any references to size limitations on files to be defragged. Are there any, or should I look elsewhere for clues to the problem? There are three such container files on his drive; the 1-gig and 3-gig files cause no problems. When the volumes contained in those three files are mounted, defrag of the volumes themselves is normal and successful.

Thanks.

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