I upgraded my nas machine which is based on nas4free this wednesday. Everything went smooth. I made a backup of my current configuration. I uploaded the new image and after some minutes my server reboots automatically. After this I was able to login. The upgrade procedure described to restore my previous configuration. But this failed. The browser showed me the error XML error: Not well-formed (invalid token) at line 1. I assume the encrypted version of my configuration can not be decrypted. After reading some blog posts i found this one. So i followed the steps described there to decrypt my configuration. With success. I decrypted my configuration with

openssl enc -aes-256-cbc -d -a -in <my-encrypted-config-file> -out decrypted-version.xml

I created an issue on the sourceforge bugtracker.

Restoring the decrypted configuration was no issue for nas4free. I was able to upgrade my nas4free machine to version without any big issues.