Please explain which AxCrypt version do you have used? If you are using the old version, please use the latest version AxCrypt app and try to decrypt the file again.
Please check your operating system has any pending updates. If any, please update.
Also please check whether your operating system has dot net framework 4.5 or above? If not please install the same. You can download the dot net framework here, https://www.microsoft.com/en-us/download/details.aspx?id=30653 .
Then uninstall the AxCrypt app and install the latest version of the AxCrypt app. You can download the same from our official website: https://www.axcrypt.net/download/ . Now install the AxCrypt app and try to start AxCrypting……
Still, you are facing any issue, please provide detailed information about the issue and write a mail to firstname.lastname@example.org. We are happy to help you.