AxCrypt is a file encryption software and it requires a full write access to the path when encrypting/decrypting the files.
If the performing user account does not have the necessary access for the file path then AxCrypt app will throw the exception like what you are getting.
Please provide the necessary access(write access for the currently signed in user) to the file path and then try to encrypt/decrypt the files under the specified location.
For more information, please check out the link: https://support.microsoft.com/en-in/help/2623670/access-denied-or-other-errors-when-you-access-or-work-with-files-and-f
Still, if you are facing any issues, You can also send the complete error report to troubleshoot the issue and write an mail to firstname.lastname@example.org.
Please follow the detailed instructions to take the complete error report: https://www.axcrypt.net/blog/send-complete-error-report/