MakeMKV needs a specific key to decrypt the AACS 2.0/2.1 protection on 4K discs. Since new movies are released constantly, the software tries to connect to a central server to download the latest "hashed keys" automatically. The error occurs for three main reasons:
If the default server URL embedded in your software is dead, you can manually point MakeMKV to the correct repository. Go to > Preferences > General . makemkv automatic hk downloading is disabled or failed
It appears the update server is unreachable, or the local key file is corrupted. I was able to resolve this by manually downloading the latest exo file from the official forums and placing it in the MakeMKV data directory. MakeMKV needs a specific key to decrypt the AACS 2