If you receive Windows Update error 80070646 or 646 while checking for updates, the error means that Windows Installer has stopped responding.
You can run a troubleshooter that automatically diagnoses and repairs problems with Windows Installer, or fix the problem manually.
Click this button:
Fix this problem
In the File Download dialog box, click Run, and then follow the steps in the wizard.
The Microsoft Fix it wizard might be in English only, but the Fix it works for all language versions of Windows.
Follow the steps below to fix the problem manually in the registry.
These steps are intended for advanced users. If you are not comfortable changing registry settings, ask someone for assistance. Modifying the registry incorrectly can cause additional problems. We strongly recommend that you back up the registry before making any changes. For more information, see Back up the registry.
In the left pane, find and click the following registry subkey:
HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
In the details pane, find AppData. The value of this key should be %USERPROFILE%\AppData\Roaming.
If the value is not %USERPROFILE%\AppData\Roaming, right-click AppData, and then click Modify.
In the Value data box, type %USERPROFILE%\AppData\Roaming, and then click OK.
Try to install the update again. If the problem persists, repeat these steps but try using the following registry subkeys instead of the subkey in step 2:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
Error codes this applies to: