Thanks! Had similar issue after copying the crontab posted above to Windows notepad and saving. I think actual problem was the EOL character (at least it was in my case). For those that aren't familiar with this, Vi (and linux text editors in general) mark end of lines (EOL) with a 'new line' character; Windows will mark with 'carriage return' and 'new line'.
To correct, I opened config.txt with docker console vi, deleted the ^M (which is what the extra 'carriage return' character will manifest as) and then saved and restarted. Many Windows text editors (e.g. notepad++) can be configured to just use a 'new line' character at EOL if you don't want to mess with vi.
