a Listbox on a TAB panel

I have a List box on a TAB panel (code below) but I get a -60 error "not a list control" and I am trying to dim some buttons. This works on the main panel but not on the TAB panel. What gives?

    CheckListItem (panelHandle, TABPANEL_Select_box, 0, 0);
    CheckListItem (panelHandle, TABPANEL_Select_box, 1, 0);
    CheckListItem (panelHandle, TABPANEL_Select_box, 2, 0);
    CheckListItem (panelHandle, TABPANEL_Select_box, 3, 0);
    CheckListItem (panelHandle, TABPANEL_Select_box, 4, 0);
    CheckListItem (panelHandle, TABPANEL_Select_box, 5, 0);

       GetCtrlVal(panelHandle,TABPANEL_Select_box,&value);

     SetCtrlAttribute(panelHandle,TABPANEL_2_COMMANDBUTTON_2, ATTR_DIMMED,1);    //dimmed
     SetCtrlAttribute(panelHandle,TABPANEL_2_COMMANDBUTTON_3, ATTR_DIMMED,1);    //dimmed