Как мне решить эту ошибку-неправильный синтаксис рядом с ' '. В С#

Incorrect syntax near ' '.
Incorrect syntax near ' '.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.Data.SqlClient.SqlException: Incorrect syntax near ' '.
Incorrect syntax near ' '.

Source Error:
     
Line 24:         SqlDataAdapter sda = new SqlDataAdapter(query, conn);
Line 25: 
Line 26:         sda.Fill(dt);
Line 27:         conn.Close();
Line 28:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;

public partial class Controls_PeopleYouMayKnow : System.Web.UI.UserControl
{
    protected void Page_Load(object sender, EventArgs e)
    {
        PeopleYouMayKnow();
    }
    private void PeopleYouMayKnow()
    {
        DataTable dt = new DataTable();
        string query = "Select * from Userregistration R where RegisterId not in ((select F.FriendId as RegisterId  from Friends f where f.MyId =" + Session["UserId"] + "and f.Status=1) Union  (select F.MyId as RegisterId  from Friends f where f.FriendId =" + Session["UserId"] + "and f.Status=1))and R.RegisterId !=" + Session["UserId"] ;
        // "Select * from Userregistration R where RegisterId not in ((select F.FriendId as RegisterId  from Friends f where f.MyId = '" + Session["UserId"] + "' and f.Status=1) Union  (select F.MyId as RegisterId  from Friends f where f.FriendId = '" + Session["UserId"] + "' and f.Status=1))and R.RegisterId != '" + Session["UserId"]+"'"
       // string query = "Select * from UserRegistration";
        SqlConnection conn = new SqlConnection(@"Data Source=ABHISHEK-PC\ABHISHEK;Initial Catalog=FrirndsZoneDB;Integrated Security=True");
        conn.Open();
        SqlDataAdapter sda = new SqlDataAdapter(query, conn);

        sda.Fill(dt);
        conn.Close();
        
        // dt = Database.GetData(query);
        if (dt.Rows.Count > 0)
        {
             
            ProfileDataList.Visible = true;
            ProfileDataList.DataSource = dt;
            ProfileDataList.DataBind();
        }
        else
        {
 
        }
    }
    protected void ImagePeopleYouMayknow_Click(object sender, ImageClickEventArgs e)
    {
        Session["CurrentProfileId"] = (((ImageButton)sender).CommandArgument).ToString();
        Response.Redirect("Main.aspx");
    }
}