What does HDD DMA error mean?

Had a power cut today and my CCTV system started beeping and flashing "HDD DMA error" on the screen. I tried turning it off and on a few times but it still kept doing it so I removed the HDD and hooked it up to my laptop in an external drive caddy, it seemed to be fine, the laptop recognised it and I... show more Had a power cut today and my CCTV system started beeping and flashing "HDD DMA error" on the screen.
I tried turning it off and on a few times but it still kept doing it so I removed the HDD and hooked it up to my laptop in an external drive caddy, it seemed to be fine, the laptop recognised it and I could copy files to/from the drive no problem.
I formatted the drive hoping it might cure the problem and reinstalled it back in to the CCTV DVR and it's still doing the same thing?
Any ideas?
I looked up DMA error but I'm still not 100% sure what it even means.
Thanks.
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