Error message when attempting to save an email message or attachment directly to a WebDrive mapped drive: “The message interface has returned an unknown error.”
To fix this error, disable a feature called “Robustified UNC” by using the Registry (regedit). Open regedit and navigate to the following location and make the change noted below:
Outlook 2007 Key
Outlook 2010 Key
Find the value named: DisableRobustifiedUNC
Ensure the value type is: REG_DWORD
Make the value: 1
This will disable the Robustified UNC feature. You will want to restart your computer after making this registry change.
The “Robustified UNC” feature involves the security measures used when opening a file, especially a .tmp file.
Disabling the “Robustified UNC” feature may also fix issues with slow performance when opening/saving files that are located on a network share.