custom self populating listbox

Hi there,
I have a problem with a custom self populating listbox control I try to make
When I add this to my formview :
<avi:mycoDropDownList ID="GW_Voorzitter" Width="450px" runat="server" whereValue='1' DataValueField="id" DataTextField="CONCAT(naam,' ',voornaam,' (',m_naam,')') AS naam" SourceTable="l_view"  />
the listbox fills up.
 
But when I try this (and that is what I need) :
<avi:mycoDropDownList ID="GW_Voorzitter" Width="450px" runat="server" whereValue='<%#Eval("Id")%>' DataValueField="id" DataTextField="CONCAT(naam,' ',voornaam,' (',m_naam,')') AS naam" SourceTable="l_view"  />
the listbox stays emty.
 
<%Ev ...