DropDownCheckBoxes and DropDownList

Question

Dear everyone

 

I had a DropDownCheckBoxes which the user will select multiple Provinces. Before it was a Dropdownlist I get the below error, how to solve it regards  

 

 

cannot convent from 'saplin.Controls.DropDownCheckBoxes to system.web.UI.Webcontrols.DropDownlist

 Please help

 

 

thanks in advance.