RUNDLL32 is an application that acts as a general-purpose host for a Dynamic Link Library (DLL). Several IE-related applications use RUNDLL32. For example, Java uses RUNDLL32 to launch an URL within IE.
Because you get the error regardless of the browser you use, you might have a corrupted RUNDLL32 file. Try deleting the existing copy in %systemroot%System32. This will force Windows File Protection to replace it with a fresh copy from the WFP cache.
If this doesn't work, it means you might have installed an application that made incompatible Registry entries that affect RUNDLL32. You may want to review any changes you made prior to experiencing the problem.
You can also try searching the Registry looking for values that contain RUNDLL32. Your looking for instances where IE or another browser might start an application.
This was first published in April 2001