Error 1386: The Specified .NET Class is Not Available in LabVIEW

Updated Aug 31, 2023

Reported In


  • LabVIEW
  • TestStand

Operating System

  • Windows

Issue Details

When I run a LabVIEW VI or DLL, or I run a sequence in TestStand, I get the following error:
Error 1386:
The specified .NET class is not available in LabVIEW.



This error message may also occur when you attempt to load a 64-bit .NET DLL into a 32-bit version of LabVIEW or vice-versa. If LabVIEW and the DLL are the same bitness, try the following steps:

  • Starting with Windows 7 and later, Windows can block access to an assembly. To resolve this, right-click the assembly and click Unblock on the General tab to grant an assembly full trust.


  • If the above step does not work, or if you are unsure which DLL is causing the issue, follow the steps below to allow LabVIEW access to all .NET assemblies. Please note that this approach imposes a potential security risk.
  1. Use a text editor to create a file that contains the following text: 
    <?xml version ="1.0"?>
        <loadFromRemoteSources enabled="true" />

  2. Save this file as LabVIEW.exe.config to trust all assemblies loaded into LabVIEW.
    • *Note* Text editors may automatically change the extension of your file when saving. Verify the extension by enabling "File Name Extensions" in Windows File Explorer. 
    • Screen shot for clarification of file extension names
  3. Place the file created in the same directory as the file it was created for, (E.g. a LabVIEW.exe.config file in the same directory as the LabVIEW.exe file) which is typically located in C:\Program Files (x86)\National Instruments\LabVIEW 201X\.

Additional Information

  • You can apply configuration files to LabVIEW Project files, shared libraries, or stand-alone executables.
  • When using TestStand, this error message can occur when an older version of LabVIEW is opened, and the VI was created within a newer version of LabVIEW. Close the older version of LabVIEW and open the version where the VIs were created.