如何使组合框下拉更改其列表与另一个组合框对应？

I am currently working on a small project for a business society in visual studio 2015 and SQL server. I have two comboboxes "AccountCode" and "AccountNo". I want to made "AccountNo" combobox to change its value in correspondence with the selection of a text from "AccountCode" drop down. But i get following error:I am currently working on a small project for a