Error code 0x80070646, 646, or 1606

When you try to install updates of Microsoft Office from Windows Update or from Microsoft Update, you may receive one of the following error codes.

Microsoft has release a patch for fix it at http://support.microsoft.com/kb/2258121


or you can follow description below

0x80070646  or  646 or  “Error 1606 Could not access network location %APPDATA%”

For Windows 7 and Windows Vista users
1. Click Start, and then in the Start Search box, type regedit.
2. In the Programs list, right-click Regedit.exe, and then click Run as administrator. If you are prompted for an administrator password or for confirmation, type the password, or click Continue.
3. Locate and then click the following registry subkey: from edit > find
 
    HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders

4. In the details pane of Registry Editor, locate AppData. The value of this key should be %USERPROFILE%\AppData\Roaming.
5. If the value is not set to %USERPROFILE%\AppData\Roaming, right-click AppData in the details pane, and then click Modify.
6. Enter %USERPROFILE%\AppData\Roaming into the Value data box, and then click OK.
7. Close Registry Editor.
8. Try to install the update again. If the problem persists, repeat these steps but use the following registry subkeys instead of the subkey that is specified in step 3:
   
    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders

For Windows XP users
1. Click Start, and then click Run.
2. In the Open box, type regedit, and then click OK.
3. In the Programs list, click Regedit.exe. If you are prompted for an administrator password or for confirmation, type the password, or click Continue.
4. Locate and then click the following registry subkey:

    HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders

5. In the details pane of Registry Editor, locate AppData. The value of this key should be %USERPROFILE%\Application Data.
6. If the value is not set to %USERPROFILE%\Application Data, right-click AppData in details pane, and then click Modify
7. In the Value data box, enter %USERPROFILE%\Application Data, and then click OK.
8. Close Registry Editor.
9. Try to install the update again. If the problem persists, repeat these steps but use the following registry subkeys instead of the subkey that is specified in step 4:

    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders