How do you play The Spongebob Squarepants Movie Game as ISO in Dolwin

As I go through the program, I notice that the program only runs dol, elf, bin, gcm, and gmp files. I have the program and game downloaded already, but it's an ISO. Whenever I select "all files" and try to load it up into the system, I get an error message, and it doesn't even tell me why. I was under the assumption that GCM files were the same as ISO, so why isn't it loading up? Is there an ISO selector somewhere? I looked all over the internet, and cant find any .dol or .gcm files for this game.

Please help me.