Why i get this error:

The data types text and nvarchar are incompatible in the equal to operator. The field of "username" in database is text type...

This is my soruce:

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="my_answers.ascx.cs" Inherits="kontrole_login_my_answers" %>

<div style=" margin-top:-1280px; float:left;">       

<p></p>


                              <div id="question">
Add question





</div>
</div>
<asp:GridView ID="GridView1" runat="server" DataSourceID="SqlDataSource1" 

   >

</asp:GridView>
<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
    ConnectionString="<%$ ConnectionStrings:estudent_piooConnectionString %>" 
    SelectCommand="SELECT * FROM [question] WHERE ([username] = @fafa)">
    <SelectParameters>
        <asp:QueryStringParameter Name="fafa" QueryStringField="user" 
            Type="String"/>
    </SelectParameters>
</asp:SqlDataSource>