I run the official website for KN-SDExplorer, and it has the most up to date information for the programme.
Your original purchase and license is still valid. Please complete the form on the following page:https://software.technicskn7000.com/contact-us/
An email will be sent to Fred and me from that form. Fred will send your license details to you (usually within 48 hours). Fred deals with licenses and I deal with support.
In the meantime, you can download the programme on the home page here - https://software.technicskn7000.com/
The software will work in demo mode (ie one file at a time but it still works fully), until you receive and input your license details.
Regarding your original problem:
In my experience, once an SD card is corrupted it is extremely difficult to retrieve. For that reason, I always back up my SD Cards regularly to my PC using KN-SDExplorer to do so. Restoring those backups is very easy and they aren't large files usually, so keep many backups.
Corruption resulting in the sort of errors you have encountered can be caused by the degradation of the contacts on the card, by some dust on the contacts or by removing the card too early when the red light is still on, for example. Cleaning the contacts might allow you to continue using the card but it will probably need to be reformatted and started afresh (keeping backups all the time). I use a pencil rubber to clean the contacts now and then, one of those slightly abrasive ones.
I hope that helps. If you need assistance with the programme please post in the forum on the same website.