Error 63 When Communicating PC to cRIO Using LabVIEW TCP Functions

Updated Jul 25, 2023

Reported In


  • CompactRIO Controller


  • LabVIEW

Issue Details

When I establish a communication between my host computer and the RIO controller using the LabVIEW TCP function, I get the following error:

Error 63 occurred at TCP Open Connection in

Possible reason(s):
LabVIEW: Serial port receive buffer overflow.
LabVIEW: The network connection was refused by the server.



There are some troubleshooting steps to fix this error:
  1. Make sure both TCP server and client devices are assigned IP at same subnet.
  2. Make sure Windows Firewall are not blocking or disabled as described here .
  3. Make sure TCP Server VI is running before running the client.
  4. Make sure TCP/IP are enabled in VI Server of the Real Time Controller Property.
  5.   If you are using dual port RIO Controller, make sure both primary and secondary ethernet adapters are set to different subnet as described in Configure Dual Ethernet Ports on Real-Time Controllers
  6. Ensure your CPU utilization is allowing TCP communication to occur. If your CPU utilization is near 100%, you won't be able to communicate over the network.