On-line storage may be the answer
Apart from the files being able to be read by modern software, the security on your own media is very much a high maintenance issue and not always going to be done by your heirs.
A family storage facility could be the only sure answer so that future generations will be able to look back at these early days of digital imaging and still see what we all looked like.
Archiving is a much bigger problem than 99.9% of people think, even if they think about it at all.
So, having found that the problems originally stated may or may not be software related and may or may not be file corruption (my least favored), what is the best way to store images online so our decedents can check them out?