Are you sure your script (bck_medidata.txt) is installed at the referenced location (/home/jorge/JJ/) and has execute permissions?
(If you ftp'd bck_medidata.txt as well you would have 'lost' the execute attributes in the transfer).
Oh yes. And ... are you sure the script isn't running, but failing silently. There should be a log file listing what actions cron performs. On HP-UX it will be /var/adm/cron/log.
Read the man page for cron and the standard location for the log should be documented for your system.
As i said, the problem was with the script and not with the CronTab.
This script was suposed to backup a few files and send information to a script when it started and finished so i knew if it made the backup or not and when. The problem was that it wasn't writing in the right file so i didn't saw it. And as i didn't saw it, i thought that the script wasn't running, when all that was happenning was that the file was being created somewhere else.