Please follow the steps below to resolve this symptom:
1. Click Start and then click Run.
2. Enter "expand C:\Windows\i386\rundll32.ex_c:\windows\rundll32.exe" and click OK.
Note: Do not leave spaces between "rundll32.ex_" and "c:\windows\rundll32.exe".
3. Restart Windows.
For more information, please see the following solution in Microsoft's technical support website:
Title: Cannot Find the Rundll32.exe File When You Open Control Panel
Last reviewed: 25 Jan 2003