The problem is caused by a change in the Windows Server 2003 version of the free ntbackup.exe utility which comes with Windows operating systems and was first disclosed in the online security news group NTBugtraq.
The change means that backup tapes formatted using Windows Server 2003 cannot be used to restore data to Windows 2000 or Windows XP machines, according to Brian Bergin, president of IT consultants Terabyte Computers.
Microsoft confirmed that the problem affects Windows 2000 Server and Professional as well as Windows XP, and experts are questioning whether more incompatibilities will emerge.
Microsoft said the backup feature in Windows 2000 and Windows XP wrote data to removable media such as magnetic tape drives in 32K bit blocks, but Windows Server 2003's backup feature writes data in 64Kbit blocks.
According to Bergin, a manager in Microsoft's storage services group, said the problem stemmed from an "oversight" in testing data migration scenarios from Windows 2003 to the Windows 2000 and XP platforms.
Bergin discovered the problem while working on behalf of his customers, which are mostly small businesses with between eight and 12 workstations connected to a common file server.
"Typically, if I have a customer with a server that goes down, I pull the tape drive and the controller out of the server and put it in a workstation and restore the files they need. When the server comes back up, I can copy the files back. You can go from 2000 to XP and vice versa all day long, but not from Windows Server 2003," he said.
After discovering the problem in late April, Bergin reported it to Microsoft technical support. "Their initial response to me was to tell me to buy third-party backup software," he said. That has now changed, he added.
"The problem doesn't affect the integrity or reliability of the systems, but it delivers a customer experience that is inconsistent with Microsoft's intended design," Microsoft said.
Microsoft has created and is testing a fix for the problem. The company will be issuing the "correction" within days, after the fix has been tested and documented.
Third-party data backup and recovery software for Windows Server 2003 is not affected by the problem, Bergin said.
In the absence of a patch for the problem, Windows 2003 customers with backup tapes that were formatted on that platform have to copy the Windows Server 2003 version of ntbackup.exe to the non-Windows Server 2003 machine.
However, that workaround is not supported by Microsoft and may be in violation of the company's licensing agreement, Bergin said.
For organisations that have not yet formatted their backup tapes, doing the initial format on a Windows 2000 or Windows XP platform first will ensure that the tapes are formatted using 32Kbit data blocks and can be used on all the platforms, Bergin said.
Paul Roberts writes for IDG News Service