I just tried this autoupdater. Works GREAT! I love it!. But I couldn't get the 'Open With' plugin to work as At_Libitum suggested. Kept getting that same error. And being somewhat computer illiterate in some areas, I didn't understand the "Nvrmind... :S peachy with a true 64bit" edit from the same post, since I'm running a true 64bit :P
So I added an Empty Book using the add books dropdown and named it "***Calibre AutoUpdate" with author "*Update, *Auto". Then I gave it a cute cover image and edited the comments field to have an explanation as well as a link to the .exe file on my computer.
Now it's the first book in my library and the link runs the update perfectly