___________________________________________
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ERROR in
action number 1
of Draw Event
for object oBattle:
Trying to use non-existing surface.
 at gml_Object_oBattle_Draw_73 (line 7) -                      surfTransition,
############################################################################################
gml_Object_oBattle_Draw_73 (line 7)

It seems that this happens when switching to fullscreen midway through a transition.

Ah interesting, yeah surfaces lose their contents in certain scenarios (like the window losing focus) I will need to put together a proper safety check for this. I imagine this might happen if you swap to full screen at any point mid fight and then finish the fight.

Should be able to fix this without too much problem in the near future, thanks for this!!

If you or anyone else would like a quick fix to this issue in the meanwhile (a more permanent fix needs to consider the tutorialization...) you can add these lines to the draw end event of oBattle. This fix will also be in the new version I'll be uploading shortly. This will remove the crash, but will skip showing the transition if you change screen focus.