Sounds like a corrupted file or perhaps a disk error, unfortunately. Probably due to power interruption, or not having been closed down correctly (the age-old problem), I suspect.
Yes; you may need the original software. But it might be worth getting that HDD out and putting it in a PC, then trying to repair the file system using the usual software tools.
The DC-3 should have a USB port; I'm wondering if you could examine the HDD from there. Do you know which filing system the HDD uses? I think the OS may be Win XP.
Do you have the
manual, by the way (see Section 8.3)?
Here are a couple of links that may prove useful:-
1)
WDC2)
Sentinel