User with Mandatory Profile can log in to Windows 7 but not to Windows XP

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http://serverfault.com – I have a Windows Server 2008 domain with both WinXP and Win7 PCs. Users are usually fine to log in to either OS, but there is one user who can't login on XP. It fails to create his profile. I believe they are mandatory profiles. How can I allow this user to log in to either Windows 7 or Windows XP? (HowTos)