be warned, my next step will be placing red hot needles under your toenails to extract *FULL * details of your problem. Note this is the 16th response to your original question.
It now appears you are setting up a duplicate system on another computer. This is not a backup as such.
The dental system itself is very old (must be if dos), as is the copying method, again being dos programs - PKZIP/PKUNZIP. When written, none of these were that forward compatible. e.g. quite possibly only dot-matrix printers are supported.
I would look at the os and disk format method on both source and target computers. Suspect the target hdd cannot be written to by PKUNZIP, because it is formatted differently to that of the source hdd.
Regarding backup security, for a commercial system, I would have rotating daily backup sets for each day used (e.g. Mon to Fri, or Mon to Sat) . Keep offsite if possible.
Also test they restore properly, before needing in earnest and finding it fails.
There is nothing to stop you setting up your own backup to an usb stick
Good Luck - Keep us posted.