Hi There
This behavior occurs because the Extensible Storage Engine (ESE) database that is used by the Microsoft Software Update Services (SUS) 2.0 version of the Automatic Updates service is opened exclusively by the operating system. Therefore, the backup program cannot read the %Windir%\SoftwareDistribution folder to build a backup image.
You can try the Open File Option which is a seperate add on. Or you can exclude the file. You will however need to determine if the file is critical or not.
Regards,