TM5-900 responsed script error when using velocity mode

[selina4715]

Hi! I'm an engineering student from Taiwan.
Sorry that the issue is not exactly a "ROS issue".
I tried to use Listen node in TMFlow connected to a Windows PC (QT 5.12.11)
I used the codes in tm_driver not including anything related to ROS. (e.g. tm_command.cpp, tm_communication.cpp)

I can successfully connect the PC and TM robot, read the state of the robot, and send PTP/PVT commands to the robot.
But I received the response of script error when I tried to start the velocity mode (using the function std::string TmCommand::set_vel_mode_start(VelMode mode, double timeout_zero_vel, double timeout_stop) in tm_command.cpp.

The blue-circled one is the script I send to the robot, and the red-circled one is the response I received.

What should I do to fix it?