Good that this worked for this example. I doubt that you get this error message because of the file's origin (or the labels). If this variable really exists in your data frame, I guess it must be your second idea: the way you are referring to the variable.
To be able to help you answer your question, I would need a minimal repr oducible ex ample . "The goal of a reprex is to package your code, and information about your problem so that others can run it and feel your pain. Then, hopefully, folks can more easily provide a solution." (FAQ: What's a reproducible example (reprex) and how do I do one? )
A minimal reproducible example consists of the following items:
A minimal dataset, necessary to reproduce the issue
The minimal runnable code necessary to reproduce the issue, which can be run
on the given dataset, and including the necessary information on the used packages.
Let's quickly go over each one of these with examples: