When you try to open the Add/Remove Programs utility in Microsoft Windows

RESOLUTION
To resolve this issue, use the Windows System File Checker tool (Sfc.exe) to clear the file cache and to replace protected system files with their correct versions. To do this, follow these steps: 1. Click Start, and then click Run.
2. In the Open box, type cmd, and then press ENTER.
3. In the Command window, type sfc /purgecache, and then press ENTER.
4. In the Command window, type sfc /scannow, and then press ENTER.

A Windows File Protection window appears, displaying the progress of the file system scan.
Note You may be prompted for your Windows 2000 CD-ROM. Insert the CD-ROM into the CD-ROM drive or DVD-ROM drive, and then click Retry.

Another solution:-

If you click START and then type C:WindowsSystem32rundll32.exe’ (without quotes) and press enter, what happens?
If it says its missing, try this:

1. Download a copy of rundll32.exe from this location: rundll32.exe **

2. Extract the file on your desktop, right click it and select ‘copy’
3. Click START
4. Click ‘Computer’
5. Double click ‘Local Disk (C:)’
6. Double click ‘Windows’
7. Double click ‘System32’
8. Right click in any of the white space and select ‘Paste’
9. Restart your computer