Find and navigate to the RiD.jar file on your computer, then RIGHT click RiD.jar, select "open with" from the menu, then select "Choose Program". At the next "Open With" display, place a CHECK mark in the "Always use the program to open this type of file", then click on the button to "browse" or "browse/open with another program", then navigate to and double click on "Program files\Java\Jre\bin\javaw.exe"

Hope this helps.