Error converting data type nvarchar to numeric

 protected void  Update(object sender, EventArgs e)
        {
            foreach (GridViewRow row in gvStudeff.Rows)
        {
            if (row.RowType == DataControlRowType.DataRow)
            {
                bool isChecked = row.Cells[0].Controls.OfType<CheckBox>().FirstOrDefault().Checked;
                if (isChecked)
                {
                    SqlCommand cmd = new SqlCommand("UPDATE studentF1 SET qi1 = @ContactName, ename = @Country WHERE idsd = @CustomerId");
                    cmd.Parameters.AddWithValue("@ContactName", row.Cells[1].Controls.OfType<TextBox>().FirstOrDefault().Text);
                    cmd.Parameters.AddWithValue("@Country", row.Cells[2].Controls.OfType<DropDownList>().FirstOrDefault().SelectedItem.Value);
                    cmd.Parameters.AddWithValue("@CustomerId", gvStudeff.DataKeys[row.RowIndex].Value);
                    this.ExecuteQuery(cmd, "SELECT");
                }
            }
        }
        btnUpdate.Visible = false;
        this.BindGrid();
   
        }

where qi1 (numeric(10,1)