Forms Data Controls :: Maintaining Selected Values In DropDownList While Paging In GridView

I have a problem with keeping the selected values in DropDownLists in rows in GridView while paging. I have this code behind:

private void RememberOldValues()
{
ArrayList LinijaIDList = new ArrayList();
int index = -1;
foreach (GridViewRow row in GridView1.Rows)
{
index = (int)GridView1.DataKeys[row.RowIndex].Value;
if (Session["equal_ITEMS"] != null)
LinijaIDList = (ArrayList)Session["equal_ITEMS"];
if (row.Cells[0].Text == lineTextBox.Text)
{
if (!LinijaIDList.Contains(index))
LinijaIDList.Add(index);
}
else
LinijaIDList.Remove(index);
}
if (LinijaIDList != null && LinijaIDList.Count > 0)
Session["equal_ITEMS"] = LinijaIDList;
}
protected void Button1_Click(object sender, EventArgs e)
{
//Session["equal_ITEMS"] = null;
RememberOldValues();
GridView1.AllowPaging = false;
BindGrid();
//RePopulateValues();
DataTable dt = new DataTable();
dt.Columns.Add(new DataColumn("LinijaID", typeof(int)));
dt.Columns.Add(new DataColumn("Ime", typeof(string)));
ArrayList LinijaIDList = (ArrayList)Session["equal_ITEMS"];
//if (LinijaIDList!=null)
//{
foreach (int LinijaID in LinijaIDList)
{
foreach (GridViewRow row in GridView1.Rows)
{
DropDownList Ime = GridView1.FooterRow.FindControl("ImeDropDownList") as DropDownList;
int rowID = (int)GridView1.DataKeys[row.RowIndex].Value;
//string Name = row.Cells[1].Text;
string Name = Ime.SelectedValue;
if (rowID == LinijaID)
{
DataRow dr = dt.NewRow();
dr["LinijaID"] = LinijaID;
dr["Ime"] = Name;
dt.Rows.Add(dr);
}
}
}
GridView1.AllowPaging = true;
Session["equal1"] = dt;
Response.Redirect("CheckedRowsPage1.aspx");
}
// else
//{
// GridView1.AllowPaging = true;
// Session["equal1"]=null;
// }
}

When I insert a value in the TextBox2 and want to select only the rows from the GridView from different pages which have value in the first column the same as the value in the TextBox2, after clicking on Button1 I get this error:

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

[Code]....