When those text boxes are empty, that's what the editor sees. 24x24 is the default resolution, 500 is the default speed, and 0 is everything else. That means, if your sprite sheet matches those values, you
can leave the text boxes empty.This is the cause of the looping error:
For example, if a CO has 4 frames, it's identified as
0, 1, 2, 3, not 1, 2, 3, 4. So Starting Frame and Loop Back To are empty (they are most of the time) and Ending Frame would be 3.
However, when you make an OCO, you only need to specify Bank and Object (unless it's the water eye or other huge monsters), and you probably already know that.
I recommend this to anyone:
Whenever you don't know what something does or you need to clarify, always do that first.