I understand your situation, but think about it logically. You write “I encrypted a new file with the same passphrase and it dycrypts with not problem” and then “All other files from three years ago to the one from last week all have the same problem“.
You also say that you’ve not changed the software (and I should add, there are no reports at all of any incompatibilities between AxCrypt versions that would cause this kind of symptoms).
My conclusion really has to be that the passphrase you used for the new file is in fact not the same passphrase as the one used three years ago. All this assuming that the message you’re getting is really AxCrypt saying that the passphrase is wrong. Just to ensure we’re talking about the same thing, you might want to send a screen shot of the error dialog.
Do consider that spaces are significant, as is upper/lower case.