Please check your system, whether you have installed both the versions(1.x and 2.x) of AxCrypt app? If yes, please uninstall the older one.
AxCrypt app used to check the default app for the file extension “.axx” when we start the app. That time, AxCrypt 2.x is not mapped for the .axx file extension, then the app will alert the user with an warning dialog which you got.
It is because of the AxCrypt 2.x app is not mapped as a default application for the file extension “.axx” in your system. So, please change the default application to AxCrypt 2.x for the file extension for “.axx” with the help of following links,
Now all the encrypted files with the file extension ‘.axx’ will be opened by double clicking the file. Restart the system/AxCrypt app, if required. Hereinafter, you will not get the warning alert.