Error -1967353900 LabVIEW DSC Modbus I/O Server Failed to Allocate a Serial Port

Updated May 5, 2023

Reported In


  • LabVIEW
  • LabVIEW Datalogging and Supervisory Control Module

Issue Details

I'm using ModBus IO Server in LabVIEW DSC module to communicate with a device using a RS-485 to USB converter. I was able to install the converter driver and communicate using the converter vendor's application, but when I go to LabVIEW, the bound variable in my VI returns the following error:

Error -1967353900 ocurred at Shared Variable in

Possible reasons: 

LabVIEW DSC: (Hex 0x8ABC8FD4) The Modbus I/O server failed to allocate a serial port. Ensure that the specified serial port is available.

This error or warning occurs while writing the following Shared Variable


How can I troubleshoot this error?


That error occurs when the NI Variable Engine cannot allocate the serial port to perform the modbus communication. Here are some troubleshooting steps you can try: