Cannot Find Rundll32.exe Error Message
1. Search your drives and locate a copy of the file 'Rundll32.exe' if you are receiving the error message, 'Windows cannot find C:\Windows\Rundll32.exe. Make sure you typed the name correctly and try again.' A copy of 'Rundll32.exe' is likely found in the folder 'C:/Windows/ServicePackFiles/i386.'
2. Right-click the file and choose 'Copy.'

3. Navigate to the folder 'C:/Windows/System32.' Right-click in the folder and choose 'Paste.' If the file already exists, choose to overwrite it; it may have been corrupted.
4. Restart the computer.
Illegal Operation Error Message
5. Click 'Details' if you've received the error message, 'Rundll32--This program has performed an illegal operation and will be shut down.' The message reports a 'General Protection Fault' in module 'MMSYSTEM.DLL.'
6. Open 'Notepad,' or any text editor, and navigate to 'C:/Windows/system.ini.'
7. Add the line 'drivers=mmsystem.dll' (no quotes), and save the file.
8. Restart the computer.
Error Message at Program Start Up
9. Reinstall a recently removed program if you receive the error message, 'Error loading C:/Windows/System/filename.dll' when starting a program. If you have uninstalled a program incorrectly, a shared 'dll' file may have been removed.
10. Open 'Control Panel' and click 'Add/Remove Programs.'
11. Locate the program and click 'Remove.' During the process, a message may appear informing you of a shared file. Choose the option to keep the file.
12. Restart the Computer.
Error Message at Computer Start Up
13. Click 'Start' > 'Run' and type 'msconfig' (no quotes) in the box if you receive the error message, 'Error loading C:/Windows/System/filename.dll' when your computer boots up.
14. Click on the 'Startup' tab, then choose 'Disable All.'
15. Restart the computer. If the error message does not occur, then the error is caused by a program in the 'Startup' menu.
16. Repeat Step 1, and click the 'Startup' tab. Click the first program's box to place a check mark.
17. Restart the computer. If the error does not occur, repeat Steps 4 and 5, adding checked programs until the error returns, isolating the program causing the error.
18. Reinstall, uninstall or leave that program off the start menu.
19. Restart the computer.