"Delayed Write Fail" when copying to external Firewire drive

I've just hooked up a 300GB Maxtor DiamondMax 10 hard drive in an
external case to my machine (Windows XP Home SP2, A7N8X-E Deluxe
motherboard). One NTFS partition.

It connects fine, the case green light shows, it shows up as as drive
in Explorer.

I can copy over few files up to a few gigs fine. However, anything that
takes longer to copy - say a few minutes - and the operation stops. The
drive disconnects (case light goes amber) and a "Delayed Write Failed"
message is shown in the notifications bar.

When I check Drive --> Properties --> Hardware --> Properties,
"Optimise for Quick Removal" (disables write caching) is turned _on_.

Is this a hardware problem?

Thanks,

P.