Error -2 opening serial port - Digi Xstick ZigBee USB device

i am using Digi Xstick ZigBee coordinator. I was testing this device using some sample programs which has given in xbee_ansic_library. But after sometime i am facing the below issue & couldn’t get any clue.

Error -2 opening serial port

Can you please help to resolve this issue & what will be the root cause???

Note: I have checked with system reboot & connected with different port, but the same issue is repeating.

Are you able to access the COM port and the radio via XCTU?

Yes, able to access from XCTU.

Did you configure the XBee for API mode 1 and Explicit frames?

Did you configure the XBee for a baud rate of 115.2kbps?