no 'Unit' columns in dtPurchaseProductExp but the error show

Question

forgive me if i am asking silly question

but i can't figure it out what is wrong       

In save button, i update datatables to database

            

            {

            new SqlCommandBuilder(sa);

            sa.Update(dtPurchaseProductExp);

                

            new SqlCommandBuilder(sa1);

            sa1.Update(dtPurchaseProduct);

            }

 

i don't have 'Unit' columns in dtPurchaseProductExp but

the following error shows up

![enter image description here][1]

![these are data columns of PurcaseProduct][2]

           

![these are data columns of PurcaseProductExp][3]

  [1]: http://i.stack.imgur.com/u6mvu.jpg

  [2]: http://i.stack.imgur.com/TU7ML.jpg

  [3]: http://i.stack.imgur.com/eYzeS.jpg