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LabVIEW Load Error Code 21: External Subroutine Required (App Note)

We've had some reports of LabVIEW load error code 21: An external subroutine required for execution could not be found. This can include other error text, such as An error occurred loading VI 'Cosine' or a message saying lvanlys.dll is missing.

This error has happened in relation to loading LabVIEW-based applications like LJLogM or LJLogUD.


Generally, running the LabVIEW 7.1 Runtime Engine installer fixes the issue. If the installer runs successfully but does not resolve the issue, try restarting your computer and testing again.

If that doesn't fix the issue, check that you have LabVIEW 7.1 installed. See: Which Versions of LabVIEW Run-Time Engine Do I Have Installed?

If you're running a networked computer:

  • Please make sure lvrt.dll and lvanlys.dll are installed locally to the same drive as the LabVIEW application you're trying to run. See: Which Versions of LabVIEW Run-Time Engine Do I Have Installed?
  • Please make sure the National Instruments Math Kernel Library is installed locally to the same drive. It should be installed to National Instruments\Shared\MKL.

If lvanlys.dll can't be found:

  • Search in C:\Program Files (x86)\National Instruments\Shared\LabVIEW Run-Time\7.1
  • Otherwise, search the entire computer for it

We also have updated versions of our logging software that use a newer version of the LabVIEW runtime (2020 SP1). We anticipate fewer issues with these versions of the loggers, and they are available for both UD and T-Series logger software.

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