Ah geez, that's a strange one. I am surprised it never came up. That object is responsible for all transitions to the next room going down.
I think I have rectified it. I have added a check in the step event that now checks to ensure that the surface actually exists before copying it.
sur_newroom = surface_create(guiWidth,guiHeight);
if (surface_exists( sur_newroom ))
{surface_copy(sur_newroom,0,0,application_surface);}
It shouldn't have needed this as the line right before the copy actually creates the surface it so my only guess is it was a frame rate thing. This change should fix the bug.
Just wanted to let you know that I purchased this pack and am currently using it in a game I'm working on (hopefully this one goes somewhere lol). Anyways, here is a clip of what it is looking like:
