When sharing a printer on a Windows 2008 R2 machine (or on Windows 7 for that matter), the operation might fail with the following error message:
Printer settings could not be saved. Operation could not be completed (error 0x000006d9)
This could happen if the Windows Firewall service on the computer is stopped or disabled. Enabling the service fixes the problem!
This might seem strange at first but if file or print sharing has never been used on that computer before, the spooler service tries to contact the Windows Firewall service to configure incoming rules for File and Print Sharing. If the service is not running, the process fails with the error mentioned above.
The error message goes away once the service is started and sharing can be configured as required. Once sharing is enabled, Windows Firewall service can be returned back to its original state. As the required ports are now open, sharing will keep working fine after that.
Hope this helps!