The "Test" button always uses the saved-filepath in "From", so he's probably just trying to test a filepath that no longer exists? Maybe clicking the test-button should 1st verify the filepath, so then reporting an error?
Hi. the From file path is the file or folder that is used for the JS test. You can select a file path for this with the browse button. If the file does not exist or the file property is not present in that file, then the JS script conduct in the same way as it would if applied to a file that is no longer there or missing that property. If you click OK and then select files in the list then you can see the script in action on "real" files.