Applies to Windows 7

Windows Update error 80070646 or 646

If you receive Windows Update error 80070646 or 646 while checking for updates, the error means that Windows Installer has stopped responding.

An automatic troubleshooter is available that fixes some problems with Windows Update, and it might resolve this error for you.

Click this button:
Fix this problem
In the File Download dialog box, click Run, and then follow the steps in the wizard.
Open Windows Update, and try to install the update again.

If that didn't work, try the following steps.

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.

Open the Registry Editor by clicking the Start button , typing regedit into the search box, and then pressing Enter.‌ If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
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