We are aware of a potential issue you may encounter with recent Office Security updates. When installing these updates, the Windows Update control panel returns the error 646 or 0x80070646.
The error 0x80070646 or 646 is an MSI installer error that will only occur when the updates are installed via the Windows Update control Panel. Previous workaround to resolve the immediate problem requires the installation of the update from a standalone package from the Microsoft Download Center. We do not recommend this workaround.
If Windows Installer logging is enabled, the following line should be noted as a symptom:
|Error 1606. Could not access network location %APPDATA%\|
The problem is potentially a result of an inconsistent/incorrect environmental variable (%AppData%) as shown below:
1. Open the Registry editor. To do so, Click Start, type regedit in the Start Search box, and then click regedit.exe in the Programs list.In the User Account Control dialog box, click Continue.
2.Navigate to HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
3.The correct and default value for AppData should be %USERPROFILE%\AppData\Roaming. To change the value, double click on Appdata, then change the string in the value data field.
4.Close the Registry editor, and try again Windows Update again. (A reboot shouldnot be required.)
5.If the problem persists, repeat the steps 2 through 4 with the following registry keys:
·HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders\
·HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders\
If the issue still persist then follow the Microsoft Article
Disclaimer : The above link is linked to a third party website and we are not responsible for any inconvenienced caused.