Rundll32.exe entry point not found

I am getting this error : "Rundll32.exe entry point not found" error message when I open My Computer System Properties.
How to solve this problem ?

Thanks

These problems may occur if Windows XP SP1a or Windows Update updates the Winsta.dll file and the repair installation does not restore the Winsta.dll file correctly. These problems may also occur if a virus scanning program interferes with the installation of a service pack.

To resolve these problems, follow these steps:

1. Restart the computer in safe mode:
   
   
   
   • Restart your computer. While your computer is starting, repeatedly press the F8 key on your keyboard. On a computer that is configured to run under multiple operating systems, you can press the F8 key when the Boot menu appears.
     
   • When the Windows Advanced Options menu appears, select an option, and then press ENTER.
     
   • When the Boot menu appears again, and the words "Safe Mode" appear in blue at the bottom of the screen, select the installation that you want to start, and then press ENTER.
   
   
2. Open My Computer, and then open the C:\Windows\INF folder.
   
3. Right-click the sr.inf file, and then click Install.
   
4. When the installation process has completed, restart the computer.