Got errors "failed to open stream: No such file or directory" and "The file or directory is not a reparse point. (code: 4390)" for file, file_get_contents, scandir, etc.. Long story short, the script and the file to be read were both in the same Dropbox directory.

I didn't try to 'solve' the problem, maybe this could be made to work in the Dropbox framework. I just moved the project out of DropBox, now it works as expected.