QT 串口通信写入错误

[rookie749]

程序是正常运行一天左右然后写入错误
报错：
Debug: QSerialPort::SerialPortError(WriteError)
拒绝访问

case 2:
buff = "#000P1520T0000!";
if(serial->write(buff)==-1){
qDebug()<<serial->error();
qDebug()<<serial->errorString();
}
qDebug(buff);
serial->waitForBytesWritten(10000);
Sleep(200);
buff = "#000P1521T0000!";
if(serial->write(buff)==-1){
qDebug()<<serial->error();
qDebug()<<serial->errorString();
}
serial->waitForBytesWritten(10000);
qDebug(buff);
break;

[rookie749]

希望大神来帮帮忙