Error:: The Insert Statement ...

hi

i'm having a problem with my project we need to make for school with asp.net & c#. the problem is i'm a newbie with c#.
the project we need to make is a survey. so the problem is my first question of the survey works fine when i push the go to next it enters the data nice into my sql db and my second question loads, then I enter the answer for my second question i press go to next question and i get this error: " The INSERT statement conflicted with the FOREIGN KEY constraint "FK_Antwoorden_Gebruikers". The conflict occurred in database "GIP_enquete", table "dbo.Gebruikers", column 'Gebruiker_ID'. " I don't know how i can fix this cause im to newbie to understand whats wrong.




here is a view of my code:





Code Snippet

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using enqueteTableAdapters;

public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
int Vraag_ID = Convert.ToInt16(Request.QueryString["vraagid"]);
VragenTableAdapter VraagAdapter = new VragenTableAdapter();
lblVraag.Text = Convert.ToString(VraagAdapter.GeefVraag(Vraag_ID));

if (Vraag_ID == 1)
{
pnlVraag1.Visible = true;
}

if (Vraag_ID == 2)
{
pnlVraag2.Visible = true;
}

}
protected void btnVraag1_Click(object sender, EventArgs e)
{
//make a new user
GebruikersTableAdapter GebruikerAdapter = new GebruikersTableAdapter();
DateTime Moment = System.DateTime.Now;
GebruikerAdapter.GebruikerToevoegen(Moment);
int GebruikerID = Convert.ToInt16(GebruikerAdapter.GeefGebruikerID(Moment));
this.ViewState.Add("gebruiker_id", GebruikerID);

//send answer
AntwoordenTableAdapter AntwoordAdapter = new AntwoordenTableAdapter();
AntwoordAdapter.AntwoordIngeven(1, GebruikerID, txtVraag1.Text, null);

//go to 2nd question
Response.Redirect("Default.aspx?vraagid=2", true);
}

protected void btnVraag2_Click(object sender, EventArgs e)
{
//get back the user from question 1
int GebruikerID = Convert.ToInt16(this.ViewState["gebruiker_id"]);


//send answer
AntwoordenTableAdapter AntwoordAdapter = new AntwoordenTableAdapter();
AntwoordAdapter.AntwoordIngeven(2, GebruikerID, txtVraag2.Text, null);


when i run debug it allways stops here





//go too 3th question
Response.Redirect("Default.aspx?vraagid=3", true);
}
}

can somebody plz help me ? =(

ps: sorry for my bad english