external hard disk could break own file system after automatically sleep

I am using Ubuntu 7.10. I have a 500gb freeagent external. It works when I first restart the computer, but soon after it will give me the message "the folder contents could not be displayed. Sorry couldn't display all the contents of FreeAgent drive"

ProblemType: Bug
Architecture: i386
Date: Fri Nov 23 17:33:38 2007
DistroRelease: Ubuntu 7.10
ExecutablePath: /usr/bin/nautilus
NonfreeKernelModules: nvidia
Package: nautilus 1:2.20.0-0ubuntu7
PackageArchitecture: i386
ProcCmdline: nautilus --no-default-window --sm-client-id default2
ProcCwd: /home/sideburns
ProcEnviron:
 PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: nautilus
Uname: Linux SKYNET 2.6.22-14-generic #1 SMP Sun Oct 14 23:05:12 GMT 2007 i686 GNU/Linux