> 
> You cannot add the <asp:textbox syntax into the control in 
> the server-code, this only works from an aspx page. You have 
> to create a new textbox control and insert it into the span.
> 
> TextBox txt = new TextBox();
> span.Controls.Add(txt);
> 

Thought so. I will have to rethink my solution.

Thanks anyway to all those who helped
Clemens