Resolving a Locked Library When a LabVIEW Class is Really Only Loaded in One Application Space

Maybe this has happened to you: you’ve created several LabVIEW classes, monkeyed around with the class properties (inheritance, perhaps), and then, seemingly out of nowhere, one of your classes is now locked. LabVIEW will claim:

The library is locked for the following reason(s): This LabVIEW class is loaded in multiple application instances. Classes must be in only a single application instance to be edited.

Nonsense. You’ve never used this class anywhere else! Before you start wondering if you suffer from multiple personality disorder, try this little trick:

  1. Open up the relevant LabVIEW project and navigate to the class in question. Notice the key icon beside the class name.
  2. In Windows Explorer, navigate to the offending .lvclass file.
  3. Open the .lvclass file.
  4. Save everything.
  5. Notice how the key went away? Good.
And sometimes that’s all it takes!


  1. Hello,
    thanks for the hints.

    but what do you mean by: loaded in multiple application instances?

    Kind Regards,


    • Hi Trevilien,

      That’s the language from the LabVIEW error message. It most likely means LabVIEW thinks the class is being simultaneously accessed by more than one project. I hope that helps!


  2. Thanks a lot!

  3. Thank you!! I got this error, didn’t understand why, and couldn’t figure out how to fix it. Your instructions worked.

  4. Thanks for this! I had this exact bug and your simple trick worked.

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