KB 971677 discusses an issue when a Hyper-V differencing disk that you create in Windows Server 2008 R2 cannot be used in Windows Server 2008.
Note: you need to click in "request hotfix" on top of KB page to request the hotfix for this specific error.
A server error occurred while you try to import the virtual machine. Failed to import the virtual machine from import directory ''. Failed to add device 'Microsoft Virtual Hard Disk'. Cannot open attachment '\Filename.vhd'. Error: 'The file or directory is corrupted and unreadable.'Cannot get information for attachment '\Filename.vhd'.