How to fix Rundll32 error and what causes this?

DLL icon on Windows Vista

A Rundll32 error happens when Windows attempts to load a file and fails to do it. When this happens a message will usually pop up on the screen informing the user that a rundll32 error has occurred. There are many things that can cause rundll32.exe error, it could be a drive error, virus, undetected malware or spyware, or a faulty or incomplete software installation. Faulty or incomplete installations of software can also cause this problem.