Error in TabPage control, Object reference not set to an instance of an object

[perhapscwk]

I use below code to find the combo box controls by its name "cboseltype1" (The reason i do this is because the 1 of the name is determine by the button, so button 1 will find cboseltype1, button 2 will find cboseltype2)

It works when this combo box and button is placed inside the form but it not works when placed inside the Tabcontrol
under any TabPage1 or TabTage2, it return an error "Object reference not set to an instance of an object."

 
ComboBox cboseltypetmp = (ComboBox)Controls["cboseltype1"];
 
cboseltype = cboseltypetmp.SelectedIndex;