The error message in question indicates that the file is severly damaged, beyond repair. You should try to locate an older version or a backup of the file.
This can happen in circumstances like you describe, where the system is shutdown or crashes, or media is removed, during an encryption operation. This is not unique to AxCrypt, it can happen to any software when it is writing data to disk.
AxCrypt version 2 has some more safeguards against this kind of situation. It does not happen often, but it does happen every now and then. Most often due to USB drives being removed to quickly without using the “Safe Remove” feature of Windows.