Easiest SQL Question Ever... I Just Can't Work It Out

 I am hoping to pass an auto incrementing number the the database. From the aspx page, I have the following code, but the insert statement does not work as it should right now. Everything worked fine until I added "rank_order" in and the SQL parameters. What am I doing wrong?
 
Thanks so much :)
  <asp:SqlDataSource ID="dsConcepts" runat="server"
SelectCommand="SELECT ID, Name FROM Concepts WHERE ID=@ID"
UpdateCommand="UPDATE Concepts SET Name=@Name WHERE ID=@ID"
InsertCommand="INSERT INTO Concepts (Name, courseID, rank_order) VALUES (@Name,@CID, @rank )">
<InsertParameters>
<asp:QueryStringParameter Name="CID" DefaultValue="-1" QueryStringField="CID" />
</InsertParameters>
<InsertParameters>
<asp:QueryStringParameter Name="rank" DefaultValue="Select Max([rank_order]) + 1 From Concepts WHERE courseID=@CID" QueryStringField="rank" />
</InsertParameters>
<SelectParameters>
<asp:QueryStringParameter Name="ID" DefaultValue="-1" QueryStringField="ID" />
</SelectParameters>
</asp:SqlDataSource>