A simple non MVC crud application, problem with update

Hey
I am trying to create a pretty simple app with crud functionality to be deployed on Azure. That's why I use asp.net 3.5 and why I can't use MVC (currently not supported).
It uses StorageClient and the listing and adding a new entry works fine. The basic aspx form looks like this

<form id="editDepartmentForm" action=""> <h2>Edit Department</h2> <dl> <dt><label for="txtDepName">Name: </label></dt> <dd><asp:TextBox ID="txtDepName" runat="server"></asp:TextBox></dd> <dt><label for="txtDepDescription">Description: </label></dt> <dd><asp:TextBox ID="txtDepDescription" runat="server"></asp:TextBox></dd> <dd> <br /> ...