I need to delete a row from my database

here its my code

        private void buttonDelete_Click(object sender, EventArgs e)
        {
            SqlConnection thisConnection = new SqlConnection(@"server=(local);Integrated security=true;" + "database=NLHdatabase");
            //
            SqlDataAdapter thisAdapter = new SqlDataAdapter("SELECT DoctorID,LastName,FirstName,Specialty  FROM Doctors", thisConnection);
            //
            SqlCommandBuilder thisbuilder = new SqlCommandBuilder(thisAdapter);
            //
            DataSet thisdataset = new DataSet();
            //
            thisAdapter.Fill(thisdataset, "Doctors");
            //
            
                DataColumn[] keys = new DataColumn[1];
                keys[0] = thisdataset.Tables["Doctors"].Columns["DoctorID"];
                thisdataset.Tables["Doctors"].PrimaryKey = keys;
                DataRow theRow = thisdataset.Tables["Doctors"].Rows.Find("DoctorID"); //-->[color="#FF0000"]HERE[/color]
            // 



            
                foreach (DataRow FindtheRow in thisdataset.Tables["Doctors"].Rows)
                {
                    if (FindtheRow["DoctorID"].ToString() == comboBoxdeletedoctor.Text)
                    {
                        //  theRow["DoctorID"] =  comboBoxdeletedoctor.Text;
                        //  theRow["LastName"] = textBoxFN.Text;
                        //  theRow["FirstName"] = textBoxNAme.Text;
                        //   theRow["Specialty"] = comboBoxSpeciality.Text;
                        FindtheRow.Delete();
                        
                        thisAdapter.Update(thisdataset, "Doctors");
                        FindtheRow.AcceptChanges();
                    }
                    
                    thisConnection.Close();
                    
                }
            
    

            Administration main = new Administration();
            main.Visible = true;
            main.Activate();
           
            textBoxFN.Clear();
            textBoxNAme.Clear();
            
            this.Hide();
        }

everything works fine but im getting this error
and cant get around.

<Input string was not in a correct format.> and it points where in red up

And when i delete that row i get this
<<<<Collection was modified; enumeration operation might not execute.>>
here its the code

private void buttonDelete_Click(object sender, EventArgs e)
        {
            SqlConnection thisConnection = new SqlConnection(@"server=(local);Integrated security=true;" + "database=NLHdatabase");
            //
            SqlDataAdapter thisAdapter = new SqlDataAdapter("SELECT DoctorID,LastName,FirstName,Specialty  FROM Doctors", thisConnection);
            //
            SqlCommandBuilder thisbuilder = new SqlCommandBuilder(thisAdapter);
            //
            DataSet thisdataset = new DataSet();
            //
            thisAdapter.Fill(thisdataset, "Doctors");
            //
            
                DataColumn[] keys = new DataColumn[1];
                keys[0] = thisdataset.Tables["Doctors"].Columns["DoctorID"];
                thisdataset.Tables["Doctors"].PrimaryKey = keys;
            



            
                foreach (DataRow FindtheRow in thisdataset.Tables["Doctors"].Rows)
                {
                    if (FindtheRow["DoctorID"].ToString() == comboBoxdeletedoctor.Text)
                    {
                        
                        FindtheRow.Delete();
                        FindtheRow.AcceptChanges();
                        thisAdapter.Update(thisdataset, "Doctors");
                        
                    }
                    
                    thisConnection.Close();
                    
                }
            
    

            Administration main = new Administration();
            main.Visible = true;
            main.Activate();
           
            textBoxFN.Clear();
            textBoxNAme.Clear();
            
            this.Hide();
        }