Problems with cron script and TERM definition using top command
You can try something like:
TERM=vt100 top -b -n 1
This will set the TERM variable to execute with the "top" command.
But your underlying problem is that your termcap database is incomplete or broken. I don't have a Debian machine to look at, but on an Ubuntu box, the "dumb" termcap info is in the file /usr/share/terminfo/d/dumb. This file is part of the ncurses-base package on Ubuntu 8.04 and 10.04. On RHEL, it's part of the ncurses package. Perhaps your installation is simply missing this file?