USB drive keeps becoming "Read-only file system"

[Hannuman Bull <hannuman@bullwebsystems.com>]

I have a USB/Firewire external SeaGate 400 GB hard drive.  I'm using it 
with BackupPC to make backups of 7 computers on my network.  I have been 
unable to get a single network backup completed.  During the backup, I 
notice a change in sound from the hd and the gkrellm monitor for sdb 
goes flatline.  

The  "mount" commands shows the drive is still online:
   /dev/sdb1 on /var/lib/backuppc type ext3 (rw)

When I "ls" the directory, I get nothing.

When I try to write to the directory (ex. "touch test.txt"), I get:
   touch: cannot touch `test.txt': Read-only file system

After typing "dmesg", I get a few pages of errors related to the drive.  
I've included the first few and last lines below:

usb 5-1: reset high speed USB device using address 2
usb 5-1: control timeout on ep0in
usb 5-1: device not accepting address 2, error -71
scsi: Device offlined - not ready after error recovery: host 2 channel 0 
id 0 lun 0
SCSI error : <2 0 0 0> return code = 0x50000
end_request: I/O error, dev sdb, sector 321979695
scsi2 (0:0): rejecting I/O to offline device
scsi2 (0:0): rejecting I/O to offline device
usb 5-1: USB disconnect, address 2
EXT3-fs error (device sdb1): ext3_readdir: directory #2 contains a hole 
at offset 0
Aborting journal on device sdb1.
scsi2 (0:0): rejecting I/O to device being removed
Buffer I/O error on device sdb1, logical block 47594577
lost page write due to I/O error on sdb1
scsi2 (0:0): rejecting I/O to device being removed
Buffer I/O error on device sdb1, logical block 47595496
lost page write due to I/O error on sdb1
.
.
.
.
EXT3-fs error (device sdb1): ext3_readdir: directory #2 contains a hole 
at offset 0
scsi2 (0:0): rejecting I/O to dead device
EXT3-fs error (device sdb1): ext3_readdir: directory #2 contains a hole 
at offset 0
scsi2 (0:0): rejecting I/O to dead device
EXT3-fs error (device sdb1): ext3_readdir: directory #2 contains a hole 
at offset 0

I've switched between the firewire and usb, but still get the same 
symptoms. 

I'm using udev with the following /etc/fstab entry:
/dev/ext-hd_sg400 /var/lib/backuppc ext3 defaults       0       0

Debian Sarge
Debian GNU/Linux, kernel 2.6.8-2-686-smp
Intel P4 3.4 GHz with Hyperthreading

I don't know what else to try.  Any help would be greatly appreciated.

Thanks,

Hannuman