XCOPY suddenly started missing folders

Quoth-Raven

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Jul 27, 2014
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I use an XCOPY command to perform backups and it used to work fine. Suddenly I noticed that some files weren't being backed up. On further investigation I found it was any folders or files in folders beginning with the letters o-z. Anything in folders a-n work fine.
I created new folders called 'a' and 'y' and ran the XCOPY command and the 'a' folder copied but the 'y' didn't,
I copied all the files to a new folder called 'source' and altered the XCOPY command to send them to a folder called 'destination' and all the files copied fine.
I then copied all these files back into the original folder overriding the originals, ran the XCOPY command again, and still all the folders o-z failed to copy again.
If I use an XCOPY command that specifies the folder name it works fine, but as I'm often adding and deleting folders this is not an ideal solution.

I've tried using robocopy but it makes no difference.

I've posted this question in other forums so to head off any other suggestions, my Windows 7 installation is fine, the files do not have a system or hidden attribute and I use an /h switch anyway so this shouldn't be a problem. The hard drive is error free and is defragmented on a weekly schedule and I've rebuilt the file index.

Any help would be appreciated.