FreeBSD 5.x and "Bad File Descriptor" errors. Why?

Hello

What follows is a description of a problem I used to have when running 
FreeBSD 5.0 and 5.1. I am not running FreeBSD right now, but I am 
considering going back to it but I need to figure out how to prevent 
this issue from happening again. My system has 2 harddrives, a 16 GB 
Seagate that I use for backups and mount it under /mnt/backup and a 40 
GB Maxtor that I am using for everything else. After the installation of 
the OS (usually about 8-12 days of running non-stop) I start getting 
"Bad File Descriptor" errors on random files all around the Maxtor drive 
and I have to go to single-user mode in order to run a full fsck on the 
system. After that, the system works, until in 8-12 days time even more 
files get "corrupted" this way and the process has to be repeated. 
Eventually, so many files are damaged that a full OS reinstall is required.

Now if not for a few things, I'd probably come to the conclusion that my 
Maxtor HD is dying on me as my Seagate drive isn't causing me any 
headaches. However this doesn't seem to be the case, as if Linux (EXT3) 
or Windows (NTFS) are used, no data loss ever occurs even if the system 
is left running for many weeks in a row. Now what exactly could be 
causing this bizarre behavior ? If this is of any help, the exact model 
number of the HD is "MAXTOR 4K040H2" and I was using UFS2 on both 
drives. Thanks in advance.

Sincerely,
Dan Naumov