Click Start, and then click Run.

In the Open box, type regedit, and then click OK.

Locate and click the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSIServer

In the right pane of the Registry Editor window, double-click ImagePath.

In the Edit String dialog box that appears, make sure that the string in the Value data box contains the correct path to the Msiexec.exe file.

The following is the correct path, where C is the drive in which Windows is installed:
C:\Windows\System32\msiexec.exe /V


Restart the computer in safe mode.

Once it is started, click Start -- Run and type in

msiexec /regserver


Press enter.

According to Microsoft this is supposed to re-register the Installer.