Hey there!
There is a bug when you right click a parameter, don't enter a value, and then click on cancel.
I get this message everytime:
___________________________________________
############################################################################################
ERROR in
action number 1
of Other Event: User Defined 2
for object obj_fl_slider_knob:
(null) argument 1 incorrect type (undefined) expecting a Number (YYGR)############################################################################################
gml_Object_obj_fl_slider_knob_Other_12 (line 4)
gml_Object_obj_fl_slider_Other_12 (line 7)
gml_Object_obj_ui_slider_hor_Step_0 (line 6)