Oh, I see. I was making two assumptions that I kind of don't feel bad about making;
- That all of the red boxes needed to be cleared;
- That the red boxes were for clearing, as opposed to moving to the goal. (I was trying to move myself to the goal.)
The second assumption is in fact given pretty explicitly as text right after level 2--where it says that red boxes don't usually go on goals. Except of course that they do in Level 2.
...and in level 3, which I solved by;
- moving one of the red boxes to the right side, clearing a line of three below the yellow box, and then
- pushing the red box down one space onto the goal.
I suspect the point was to make a line of five red boxes and then push the yellow one onto the goal, but since I'd just learned from the previous level that I didn't need to...
I'd also, personally, avoid things like Level 4. You want people to understand the mechanics of your game, and not the incidental (and obscure) mechanics of PuzzleScript.