Error in CreateUserWizard

[skiabox]

I tried this one but I get an error :

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The code behind is

protected void CreateUserWizard1_CreatedUser(object sender, EventArgs e)
    {
        Roles.AddUserToRole(CreateUserWizard1.UserName, "Role1");

        TextBox UserNameTextBox = (TextBox)CreateUserWizardStep1.ContentTemplateContainer.FindControl("UserName");
        SqlDataSource DataSource = (SqlDataSource)CreateUserWizardStep1.ContentTemplateContainer.FindControl("InsertExtraInfo");

        MembershipUser User = Membership.GetUser(UserNameTextBox.Text);
        object UserGUID = User.ProviderUserKey;

        DataSource.InsertParameters.Add("ΚΩΔΙΚΟΣ_ΔΙΑΧΕΙΡΗΣΤΗ", UserGUID.ToString());
        DataSource.Insert();
    }

And the error I get is :

Object reference not set to an instance of an object.

Source Error:

Line 29: object UserGUID = User.ProviderUserKey;
Line 30:
Line 31: DataSource.InsertParameters.Add("ΚΩΔΙΚΟΣ_ΔΙΑΧΕΙΡΗΣΤΗ", UserGUID.ToString());
Line 32: DataSource.Insert();
Line 33: }

Any help?
Thanx!