I used an exapmple from a tutorial to sort columns in treeview. It works for 2nd and 3rd column, but not for the 1st column. If I click on the heading I get this Error:

I used an exapmple from a tutorial to sort columns in treeview. It works for 2nd and 3rd column, but not for the 1st column. If I click on the heading I get this Error:

I used an exapmple from a tutorial to sort columns in treeview. It works for 2nd and 3rd column, but not for the 1st column. If I click on the heading I get this Error:

I used an exapmple from a tutorial to sort columns in treeview. It works for 2nd and 3rd column, but not for the 1st column. If I click on the heading I get this Error:

I used an exapmple from a tutorial to sort columns in treeview. It works for 2nd and 3rd column, but not for the 1st column. If I click on the heading I get this Error:

I used an exapmple from a tutorial to sort columns in treeview. It works for 2nd and 3rd column, but not for the 1st column. If I click on the heading I get this Error: