Your select parameter is probably never set. I suggest that you try to set the default value to something that exists in your database. If that makes a difference, you'll know that the parameter is never set to anything other than the default.
You can set the value of the parameter by using a controlparameter instead:
<SelectParameters>
<asp:ControlParameter ControlID="__Page" Name="UserName" PropertyName="LoggedInUser" Type="String" />
</SelectParameters>
This will get the username from a property called LoggedInUser in the codebehind.
public string LoggedInUser
{
get
{
return "RJoness";
}
}
Or you can set the parameter directly from codebehind:
SqlDataSource1.SelectParameters.Add("UserName", "RJoness");