One of Windows Backup errors that you may experience while using Windows 7 is:
The backup was not successful.
The error is: Windows Backup encountered a problem while determining additional locations of one of the users included in backup. (0x81000038)
This error usually happens if you are using Windows 7 with Microsoft Office 2000.
If you want to make sure which .msi package is causing this behaviour, you can do the following:
Edit the Windows Backup Service to “Allow service to interact with desktop“. Restart the service afterwards.
You should be notified when Backup comes across the offending msi. Just clear the message and proceed.
Solution:
Copy the DATA1.MSI from the Microsoft Office 2000 disk to the C:\Windows\System32 folder.
This should fix the 0x81000038 error.