The Cron tasks on my website run perfectly fine if I manually execute cron. However, I have the server set up to automatically run cron every hour. When cron is executed automatically it fails... every time. The error message is always about memory usage exceeding the allowed levels (which are already rather high). Most of the time, though not always, this error is thrown from the Date module. I do have a feed set up that pulls from a large Google calendar, so I've been thinking that might be the problem. But why would it succeed when run manually? I understand that when run manually it's run as my admin user, and when run automatically it runs (correct me if I'm wrong) as an anonymous user. Does that have something to do with the failure/success pattern?
Edit: Posting the actual cron command as requested
/bin/php5 -q /path/to/my/account/public_html/cron.php