Fish food not falling (tutorial help)

I managed to get to the fifth .pdf for the fish tutorial with only one small hiccup, but now I am at a completely frustrating halt. I followed the instructions exactly, saved my .cs files, saved my game files, closed and re-opened the T2D program, everything. I even went as far as to copy the code exactly from the help files included. Nothing is working. I've retraced my steps 3 times so far and can find no errors in code or T2D "edit tab" variables. I've tried putting the food bubble inside and outside of the world limit. No matter what I try, the food just won't fall! What should I do?