C# - Exception (missing Primary Key) In The Line Of Using Find() Method "Table Doesn't Have A Primary Key"

i get the following exception (missing primary key) in the line of using Find() method "Table doesn't have a primary key." I've rechecked the Database and all Primary Key columns are set correctly.

DataTable dt = p.GetAllPhotos(int.Parse(Id));
DataTable temp = new DataTable();
temp = dt.Clone();
temp = (DataTable)(Session["currentImage"]);
DataTable dtvalid = new DataTable();
dtvalid = dt.Clone();
DataRow[] drr = new DataRow[1];
drr[0] = dt.Rows.Find((int.Parse(temp.Rows[0]["photoId"].ToString()))+1);
foreach (DataRow dr in drr)
{
dtvalid.ImportRow(dr);
}
dtvalid.AcceptChanges();'