Solution to Error 646

In this article we will discuss the cause of error 646 that may occur while installing updates on a Windows computer and its solution.


When installing new updates on your Microsoft Windows Vista computer, you may receive the error code 646, stating –

“Windows has encountered an unknown problem”

and is unable to install updates.

Cause of the Error

Generally, the above error occurs when the Windows Update agent file Wups2.dll is incorrectly registered in the Windows registry. Update installation fails because the registry files that correspond to the wups2.dll are missing.

Resolution Methods

To resolve error 646, manually register the Windows Update files. If you still are not able to install updates, then download and install the Windows Update agent.

Method 1: Manually register the Windows Update files

Warning: The registry is a critical component of Windows operating systems. Perform the following steps carefully and as they are shown. Incorrectly modifying the registry may cause serious damage to your computer. As a precaution, always make a registry backup before altering its content. This will allow you to restore the registry to its last working state in case any complications arise. You may back up the registry manually or use an advanced registry cleaning tool, such as RegServe for this purpose.

To manually register the Windows Update files, perform the following steps:

  1. Click the Start menu and then in the Start Search box type notepad.
  2. Next, click Notepad.
  3. Now, copy and paste the text mentioned below in the opened Notepad window:
    regsvr32 wups2.dll /s
    regsvr32 wups.dll /s
    regsvr32 wuaueng.dll /s
    regsvr32 wuapi.dll /s
    regsvr32 wucltux.dll /s
    regsvr32 wuwebv.dll /s
    regsvr32 jscript.dll /s
    regsvr32 msxml3.dll /s
  4. Next, click on the File menu and click Save As.
  5. Select All Files from the Save as type drop-down menu.
  6. In the File name box, type register.bat.
  7. Select Desktop from the Save in drop-down list.
  8. Click the Save button.
  9. Next, right-click the register.bat on your desktop and click Run as administrator.
  10. Type the administrator password when prompted.

After you have successfully registered the Windows Update files, try to install updates. If you receive the error, proceed to the next section.

Method 2: Install the Windows Update Agent

The Windows Update agent allows you to manage which updates will be installed on your Windows computer. The Windows Update agent and the Windows Update Web site work together to provide the latest updates to your Windows computer.

To install the latest version of the Windows Update Agent, visit the Microsoft update website.