This forum has already been migrated several times to another forum software. And each time PTC had managed to ruin things, many posts were lost, attachments were deleted making posts meaningless, links like this one were not adjusted, keywording was lost, etc.
It was a shame to have to watch the sheer incompetence over and over again.
I can only guess which post or file Richard referenced here, so I'm attaching it on spec. Good luck!
Be aware that this sheet will attempt to recover legacy worksheets (Mathcad 15 and below) only. Its of no use for corrupted Prime sheets!