it is sort of unlikely that you notice an error when using cron and not when used manually, still; try this module Schedule::Cron instead of regular cron,
try running in debug mode and step thru the process, or write a loging functionality so you log every thing to a log you can review the process as it flows.
the cron jobs that I have are setup to direct the std output to a log file / dump file, as cron sends all the errors to the mailbox.
hope this helps, Rana