I'm a bit unsure about the syntax of your ctrontab entry.
As far as my experience goes, they look like the one from the previous poster.
Special care must be taken to set all file paths correctly. To be safe, you should even consider to do this for system files.
At least things should be tested thoroughly and file paths are to be the first suspects when things are failing.
Always begin with running the script from the command line. Only put it in crontab when cli execution works.
One of the many explanations on the web: http://v1.corenominal.org/howto-setup-a-crontab-file/