When you save the VI, you have the option to remove the diagram (the source code) and be left with the compiled code. The problem is that when you want to run the VI in the newer version, it needs to be recompiled, and for that, it needs the diagram.
You need the original VI (the one with the diagram). If that wasn't kept, you will need to rewrite the VI.
You should always keep at least one copy of the source code somewhere.
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