Your problem is very confusing rbincola.
Have you still got your old machine? If so, try decrypting them on there and then copying them over unencrypted on a USB stick to the new machine. If they refuse to decrypt on your old machine then the files have become damaged somehow. This happens to all files eventually – it makes no difference whether they’re encrypted – see 3 paragraphs down.
If you no longer have your old machine then please post a screenshot of the error message.
You say that the files are “in a folder that was de-crypted” yet you said that you have “used the old version of Axcrypt for years”. Did you decrypt them with the old or new version? If the problems occurred after using the old version then it’s got nothing to do with the upgrade.
All files on a computer, whether encrypted or unencrypted, suffer from a phenomenon known as bit rot. That means your files become naturally damaged the longer you leave them on a computer. That is why backups are so important, particularly so if it’s your ‘life’s work’.
You must follow the 3-2-1 backup rule if your files are important. Imagine what would happen if your computer is stolen or damaged in a fire/flood/earthquake or if you just dropped it on the floor! For this reason always backup your files; the general rule is: if they’re not backed up, they can’t be that important.
Make sure that you’re using the latest version (2.1.1536) of AxCrypt.