VS C# Not a valid boolean

I have this loop the examines a check box in a datagridview.  On my development computer it works fine. I just loaded this program onto a target computer to test and if they put a check in the box and this loop is executed we get the message "String was not recognized as a valid Boolean". How do I track down this error? What could it possibly be?

            foreach(DataGridViewRow row in dgvOpenSalesOrders.Rows)
            {
                try
                {
                    if  ( Convert.ToBoolean(((DataGridViewCell)row.Cells[7]).Value.ToString()) == false)
                    {
                        WriteRecord(Convert.ToDateTime(((DataGridViewCell)row.Cells[0]).Value.ToString()), Convert.ToDateTime(((DataGridViewCell)row.Cells[1]).Value.ToString()), ((DataGridViewCell)row.Cells[2]).Value.ToString(),
                         ((DataGridViewCell)row.Cells[3]).Value.ToString(), ((DataGridViewCell)row.Cells[4]).Value.ToString(), ((DataGridViewCell)row.Cells[5]).Value.ToString(),Convert.ToDecimal(((DataGridViewCell)row.Cells[6]).Value.ToString()),Convert.ToBoolean(((DataGridViewCell)row.Cells[7]).Value.ToString()), TRNSDATE, TRNSFLAG);
                    }
                }
                catch (Exception ex)
                {
                    string eMsg = "003: ERROR: " + ex.Message;
                    if (StackTraceWanted) eMsg += "\n" + ex.StackTrace;
                    MessageBox.Show(eMsg);
                }
            }