Getting error when am inserting drop down list value in db

Question

am binding data  to drop down from database,

then i want to insert those selected value in another table

but am getting error   as

 

An exception of type 'System.NullReferenceException' occurred in App_Web_2himjopn.dll but was not handled in user code

Additional information: Object reference not set to an instance of an object.

 

 @Html.DropDownListFor(u => u.AccountListModel, Model.AccountListModel, new { @style = "width:150px;height:22px;", @id = "ddlAccount" })

getting error here 

 

 

but values are saving in database table