Argument Exception when selecting object

Hey guys,

I have a Rope component for handling 2D rope creation for a platformer I'm working on. It also has a custom editor so I can display the rope spline in the Sceneview and to structure the Inspector more clearly.

Everything about it works fine, but when any Rope object is first selected, I get the following error: "ArgumentException: Getting control 0's position in a group with only 0 controls when doing Repaint Aborting"

Here is the section of code, up to the line causing the error. Nothing omitted: public override void OnInspectorGUI() {

             Rope rope = (Rope)target;
             if (rope.makingRope == null)
             {
                 //Draw the Spline GUI stuff.
                 serializedObject.Update();
                 EditorGUI.BeginChangeCheck();
 
                 bool includeColliders = GUILayout.Toggle(rope.includeColliders, incColContent);

I've read a few similar questions, but none of them has applied in my case, or had a solution that made a lick of difference.

So, why is this happening? Again, it only happens ONCE, when the object is selected. And the error is convinced it's happening in that GUILayout.Toggle.