Rundll.exe or Rundll32.exe

Found in the file, or in Windows 98 Second Edition.

You may receive random general protection (GP) fault error messages in Mmsystem.dll. You may also receive one of the following error messages:

Rundll(32) - This program has performed an illegal operation and will be shut down.
Clicking the Details button reveals a message similar to one of the following:
RUNDLL(32) caused a General Protection Fault in module MMSYSTEM.DLL
This error message is more likely to occur after you use the Add New Hardware tool in Control Panel.

This problem can occur if the "drivers=mmsystem.dll" line is missing from the [boot] section of the System.ini file, or if mmsystem.dll is missing or corrupt.

This problem can also occur when the System.ini file has been replaced with the System.cb file.

When you try to open the Network tool in Control Panel, nothing may happen, or you may receive any of the following error messages:

Rundll caused an invalid page fault in netdi.dll, or
Rundll32 caused a general protection fault in krnl386.exe

This behaviour may also occur when you right-click Network Neighbourhood and then click Properties.

This is caused if the Netdi.dll file or the Netos.dll file in the Windows\System folder is missing or damaged

When you start Windows 98, you may receive the following error messages:

Error loading powrprof.dll.
The system cannot find the file specified, or
Error Starting Program
A required .DLL file, POWRPROF.DLL was not found.

These error messages may occur even if you disable LoadPowerProfile on the Startup tab in the System Configuration Utility tool (Msconfig.exe).

This occurs if the Powrprof.dll file in the Windows\System folder is missing or damaged.

From the examples above there is a discernible pattern. Rundll or Rundll32 errors are generally caused when the dynamic link library (dll) utilised is missing or corrupt. The solution is to extract that dll from the windows cab files in Windows 95, or use System File Checker (SFC) in windows 98.