On free hosting you're limited to 1 cron per 5 minutes - if any crons are set up that there are times they will run within 5 minutes of each other (such as a 5 minute cron executing at *:00, *:05, *:010, etc and an hourly cron executing every hour at 0 minutes after the hour), they will automatically purge out of the account.
You'd have to upgrade to Prime, Illuminated, Premium, or VPS to allow crons every minute.