When you try to read row from one table and add to another table, if you get the exception i.e. ""This row already belongs to another table". For example:

foreach (DataRow drWrite in dtRead.Rows)
{
    dtWrite.Rows.Add(drWrite); //Error thrown here.
}

There are two solution for above exception:

1. You need to create a "NewRow" with the values from reading row of reading table first. For example

   DataRow drWrite = dtWrite.NewRow();
   drWrite["Col1"] = dtRead.Rows[0]["Col1"];
   drWrite["Col2"] = dtRead.Rows[0]["Col2"];
   dtWrite.Rows.Add(drWrite);

    

2. You can also use "Add" which takes an array of values. For example

   dtWrite.Rows.Add(drWrite.ItemArray);

   or

   dtWrite.ImportRow(drWrite);

    

Hope it helps. Happy Coding!!