Are you trying to open the file by double clicking?
You might be able to resolve that error by manually decrypting it – right click on it and press Stop Securing. Just remember to encrypt it again once you’ve finished with it!
I’ve never seen that message before in AxCrypt and if the manual decryption I’ve suggested doesn’t work then somebody from AxCrypt will be along shortly to answer your question now that there’s sufficient information on the error (the screenshot).
I, like most others on here, am a user and have never encountered that error in AxCrypt.
Having programmed a few systems myself I can see from that message normally means the problem is that the compressed size of doesn’t match the size of the original. It’s easy for AxCrypt to resolve.