One comment: you have set Use Preload to true in your connection string. Use Extended Types = false; the exception changes to: System.
This is a legacy feature and it's strongly recommended not to use it (it have been removed from the upcoming major version 3.0). Invalid Cast Exception occurred HResult=-2147467262 Message=Specified cast is not valid.
In this article however, I'll show you how a Grid View control can be used to update (edit), delete and insert data in a remote SQL Server table. Attach the Grid View with the Sql Data Source control, the way we have shown the link above.
After you have run the website, you will see the Grid View showing details of employees in tabular format.
Many a times in our applications we use primary keys to get control of the particular record in the gridview.