referenced

Okay so is it possible (and if so how to go about it properly) to draw sprite items and then reference or move them individually in game when something happens? For example, lets say I have this... draw_sprite(info here); // top layer draw_sprite(info here); // mid layer draw_sprite(info here)...

I'm ill, fuzzy-headed and simply can't see what I'm doing wrong here. What does 'variable xxx only referenced once' mean? This is the gamestart event of a controller object. Am I doing something or can I blame it on the latest GMS2 update? Many thanks,