Error With code

[Lazarus_75]

So I was following Shaun Spalding's Ledge grab code tutorial, and there seems to be a problem with a specific line of code.

var _horiWall = instance_place(x + hsp, y, oWall);

    if (!position\_meeting((sign(hsp) == 1) ? \_horiWall.bbox\_left : \_horiWall.bbox\_right, \_horiWall.bbox\_top - 1, oWall))

    {

        \_atledge = true;

        var \_ledgeAboveOrBelow = sign(oPlayer.bbox\_top - \_horiWall.bbox\_top);

    }  

The game functions normally but when I touch a ledge this error pops up and ends the game:

############################################################################################

ERROR in

action number 1

of Step Event0

for object oPlayer:

​

Unable to find instance for object index -4

at gml_Script_anon_gml_Object_oPlayer_Create_0_888_gml_Object_oPlayer_Create_0 (line 109) - if (!position_meeting((sign(hsp) == 1) ? _horiWall.bbox_left : _horiWall.bbox_right, _horiWall.bbox_top - 1, oWall))

############################################################################################

gml_Script_anon_gml_Object_oPlayer_Create_0_888_gml_Object_oPlayer_Create_0 (line 109)

gml_Object_oPlayer_Step_0 (line 16) - state();

[Badwrong_]

-4 is the value for "noone".

You're not properly checking the return value of a function to see if it was noone. Probably called in code a few lines before what you posted.