Multiple Errors and an Exclamation Point for COM port in NI MAX

Updated Nov 25, 2022

Reported In


  • Measurement and Automation Explorer (MAX)



Issue Details

  • There is a yellow exclamation point over my COM Port under Devices and Interfaces in the Measurement & Automation Explorer.
  • When I right-click an existing COM Port and select Open VISA Test Panel, I receive the following error:
    • Unable to open session to "ASRL3::INSTR"
      Return Value: 0xBFFF0072
      Status Name: VI_ERROR_RSRC_BUSY      
                                                                                                                              The resource is valid, but VISA cannot currently access it. 
  • I am receiving the following errors in MAX test panel:
    • Unknown misc error
      The resource does not support this combination of parameters
  • In the General tab for the COM port, I receive the following error:
    • VISA returned this device when finding resources, and MAX was able to use 
      VISA to parse the resource name. The resource was busy, so MAX could not successfully open a VISA session to the device.


  • Close out of any program that could be accessing the COM Port. Some examples of these are listed below:
    • LabVIEW
    • HyperTerminal
    • Palm Desktop Hot Sync Manager
  • If the issue persists, disable the COM Port through its properties:
    • Windows 7/8/10: Open Control Panel and click the Hardware and Sound category. Next, select the Device Manager from the Devices and Printers category. Expand the Port category, right click the appropriate COM Port, and choose Disable. Afterwards, restart your machine, access the COM Port properties again, and enable the port.
  • Reference documentation for your hardware to verify that you have all necessary drivers installed.
    • Expand the Software category in the menu on the left side in MAX to see what drivers you have installed.
  • Reference documentation for your hardware to verify that the baud rate, data bits, parity, stop bits, and flow control you've specified in MAX are correct. 
  • Make sure that there isn't another device on the network using the same IP address. To check this, remove the ENET-232 from the Ethernet connection and ping the IP address. If there is a response to the ping, there is an IP address conflict.
  •  Change the Port Name you are having issues with to another one.
    1. Go to Windows Device manager > Multi-port serial adapters.
    2. Select the adapter and right-click to open the menu.
    3. Click on the Properties link.
    4. Open the Ports Configuration tab.
    5. Click on the Port Setting button.
    6. Select the Port Number and click OK.
    7. Click OK to apply the changes.

Additional Information

  • If you have access to Hyperterminal (included in Windows XP and earlier), you can use it to verify communication with the COM port. The following test writes to the serial port and reads from the same port (make sure you have a loopback configuration):
  1. Select Start»Programs»Accessories»Communication»Hyperterminal.
  2. Click on the Hyperterminal icon.
  3. If you are asked if you would like to install a modem, select No.
  4. You are prompted to select an icon to represent the connection you are about to define. Choose any one, and name the session.
  5. In the next Pop-Up menu, choose direct to COMx where "x" is the number of the COM Port you are testing.
  6. Set the flow control setting to None. You may leave the other settings in the next dialog box, though you can increase the speed if you like.
  7. Select File»Properties from the menu bar, select the Settings tab, and then push the ASCII Setup button.
  8. Check the option for Echo typed characters locally.
  9. Start typing. If you see double characters (that is, you see two characters for every one you type), the serial port is setup correctly and is functional.