When you upgrade your Symantec management agent client it fails to work properly and the file copy task fails unable to copy files from one system to another.
ErrorMessage: MapDriveCommand to get N/W Credentials failed value=0, error=0 On Notification server
From the client agent logs we found
<![CDATA[Command to get N/W Credentials failed.]]>
Actual cause is unknown currently investigating will most more info when available.
Right now it looks like some of the files and data gone missing for the Symantec client agent when upgrading and also it fails to update deployment solution task handler plugin.
Turn on deployment solution plug-in policy and make sure you select rule properly to upgrade the client agent with the plug-in will resolve the issue
Uninstall Symantec client agent completely and re-install fresh Altiris 7.5 client would resolve the issue.