Couldn’t load an official pak file

“Couldn’t load an official pak file” means you have not installed 2.6 patch before 2.6b. So if you don’t want to see the “Couldn’t load an official pak file” error message again, do strictly this:

– reinstall ET, so you will have the basic 2.55 patch
– install the 2.6 patch (download from here)
– install the 2.6b patch (download from here)