I also hope your drives are clean, always use a floppy drive cleaning kit in your Amiga to avoid read/write errors.
As for the HD floppy disks, there's no way to say how long the data will last on them, I don't know if usage or time makes it happen but after a while you're bound to get a read error on each of the disks. It has to do with HD media not being good at retaining data when formatted as DD. In any case it's not a really big deal, just re-write the ADF back to the disk and it should work again. I always write an ADF three times in a row, just to really burn it in there, not sure how effective it is but it doesn't hurt.
