All right, got this error when trying to edit a map I had saved (though to be fair, it did warn me with "Error loading map ;_(" once I tried to load it up a second time):
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FATAL ERROR in
action number 1
of Step Event0
for object oME_SaveMap: Variable <unknown_object>.<unknown variable>(100116, -2147483648) not set before reading it.
at gml_Script_editor_save_map
############################################################################################
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stack frame is
gml_Script_editor_save_map (line -1)
gml_Object_oME_SaveMap_Step_0
Should I send the map file to you for inspection? Also, now I see your mastery... GameMaker! That underrated tool has come such a long way.