That's the strange thing. It works fine from the command line (when running with the same user the service accounts are running as).

I've even tried putting a bunch of those commands in a batch file, and just running the batch file from xp_cmdshell. It doesn't work. But if I run the batch file from the command line it works again.

Normally I would think it's a permission error, but since xp_cmdshell (at least according to books online) runs with the credentials of the sql server agent service account, and I can log on as that service account to the desktop and run it manually with sucess, I'm not sure it's security. I can do simple things like:

...

xp_cmdshell 'dir d:\'

And that works, so I also don't think it's any obvous configuration issue either.