1. Reboot your computer and run the program again, if the error was the result of using a specific program. Sometimes a restart can fix the problem.
2. Note the name and location of the DLL, if you still have the error after reboot. Search for the DLL in question on DLL-Files.com, and download it. Save the file in the location mentioned in the error message, and try again.

3. Download an anti-spyware program, if you don't already have one, and use it. RUNDLL errors are often caused by the dastardly tricks of malevolent software, and merely fixing the one at hand won't prevent future errors. If spyware is the cause of the error, anti-spyware software will take out the perpetrator.