hello maryam, i think you dont have write permission on the drive you're trying to compile on "creating your .exe file" try to delete "Charge1.exe" from debug folders "you dont get a problem when you run it without changing the source code cuz you're running the compiled executable file!" to clean previous objects, try Build > Clean Solution, Build > Build Solution good luck maryam

Yes you can, add a new column to the datasource (DataTable??) which you are creating manually and fill data in that newly added column from datatable filled from database. Saqib

On load of your form or in any another event u can add code down below dataGridView1.Columns[index].Visible = false; //indexn is index of column which u want to hide in dataGridView