I am not really sure but could it be the way the external hard is formatted?
Not sure if that matters but I think most external hard drives come pre-formatted in FAT32.
If it comes pre-formatted to FAT32 for compatablity. If you're running Windows XP converting it to NTFS is reccomended and doesn't take much effort. Control Panel > Admin Tools > Computer Managment > Storage > Disk Managment. Right click the drive and format. Due to it's size, I'd recommend a quick format. All the full format does is search for bad sectors on the disk and recover/disable them.

I am not saying this is the problem. I am just thinking outloud here.

Or you should visit the site and then check their forum for support. Not sure what to tell you.