SqlDataSource Parameterized Stored Procedure Problem!!

[Kel]

I am currently trying to pass the SqlDataSource below a paramter set in
the code-behind (C#) My stored procedure takes one parameter @AID
varchar(25).

<asp:SqlDataSou rce ID="ListEmpSour ce" Runat="server"
SelectCommand=" dbo.usp_ListEmp s"

ConnectionStrin g="Server=(loca l);Database=Tes t;Trusted_Conne ction=yes"
SelectCommandTy pe="StoredProce dure" >

<SelectParamete rs>
<asp:Paramete r Name="AID" Direction="inpu t" Type="string"
DefaultValue="u sername" />
</SelectParameter s>

</asp:SqlDataSour ce>

Then in the codebehind I try to do this (one of many solutions I've
tried)

string strUserName = User.Identity.N ame;

ListEmpSource.S electing += new
SqlDataSourceSe lectingEventHan dler(ListEmpSou rce_Selecting);

//Event Handler:
public void ListEmpSource_S electing(object sender,
SqlDataSourceSe lectingEventArg s e)
{
e.Command.Param eters["@AID"].Value = strUserName;
}

Thanks in advance...