I used the transporter to get to the little island off the main island, and now it won't let me back on the main island, regardless of whether I complete the one level on that island or not.

Did I do the levels in the wrong order? Is that even possible?

Any and all assistance would be greatly appreciated.

Happy gaming.

You should be able to go back into the transporter and return to the main island. After you complete all the other levels, the large structure in the middle of the island becomes accessible, so you have to do all the other levels, and the order shouldn't matter. If you're still stuck, I can upload my saved games, and you can continue from one of my files.

Belated response, but for the sake of anyone else who may be having this issue... The collision detection for the transporters is very particular. Just keep nudging the character around inside the transporter and eventually it will teleport him.