Error 1601: "Windows Installer is not accessible" when installing or updating

Try the following solutions, in the order listed, until the error goes away.

1. Restart your computer, and then try installing or updating again.
2. Change the Windows Installer properties:
   1. On the Windows taskbar, click Start, then choose  Control Panel.
   2. Double-click Administrative Tools, and then Services.
   3. Locate and open the Windows Installer service.
   4. Verify that the startup type is manual and the service status is stopped. Then try installing or updating.
      
      
       
3. Download the Windows Installer, and then try installing/updating again.
4. Finally, if the error persists despite following the solutions above, follow the steps at the Microsoft site.

Here's another workaround for Windows 7 or Vista:

1. Click the Windows Start button and choose All Programs > Accessories > Run.
2. Type msconfig in the box.
3. Click the Services tab and scroll down to Windows Installer Service. Make sure the checkbox is cleared.
4. Restart your computer.
5. Close any selective startup mode messages, and repeat Steps 1 and 2 except this time type services.msc in the box.
6. Locate the Windows Installer Service and reset it to Manual. Then start it by right-clicking it or double-clicking.
7. Install TurboTax.
8. When finished, repeat Steps 1 and 2, then select Normal Startup on the General tab. Click OK and restart your computer when prompted.