Hello,
If cronjob did not work you would have more issues with directadmin tally and running backups. If your command does not work I'd rather say that's a matter of a syntax of the particular command. So please either check it with a guide for software you use there or post here so we could see it.
Anyway to check you might want to read /var/log/messages and/or /var/log/cron and redirect output of crontab task to a file.