Current situation is a disaster for scripts. I have reported my issue here:
http://forum.mikrotik.com/t/v7-18beta-testing-is-released/181371/1
… but did not yet open an issue for support. Looks like the implementation is racy, so all scripts that handle files are randomly crashing.
Sometimes even file is available for find, but remove fails anyway, something like:
/file/remove [ find where name="file/with/path" ];