The first exception indicates a broken or incomplete write of an encrypted file.
The second exception indicates an empty file or a file that is simply not an AxCrypt-file. Each AxCrypt-file starts with a fixed sequence of 16 bytes. This error indicates that the file in question does not. That’s unlikely to be due to corruption.
Do try the case with an existing file on a test file, I’m sure you’ll see the ‘save as’ dialog. Hope you have some backups!