I just found two malfunction RX64 dynamixels.
1. For the first malfunction RX64 dynamixel condition,
1.1 It is not able to be searched by the USB2Dynamixel manager.
1.2 LED turn on always after connecting power
2. For the second malfunction RX64 dynamixel condition,
2.1 LED turns on and off after connecting power. (It seems OK.)
2.2 It is able to be searched by the USB2Dynamixel manager but spending more time.
2.3 It cannot be controlled and found the error like this.
! Dynamixel access failed!
Please check USB2Dynamixel, dynaixel(s), and power connection.