...and there are many errors related to files which cannot be opened
I am getting this all the time. This is why FetchMail, ProcMail and DoveCot wouldn't work. ProcMail was creating errors but couldn't even write to it's own log file! It is also why it took me several hours to be able to write to a hard disk I had formatted to ext4, because it decided the disk belonged to 'root'.
It will probably be a file permission error again.
You should do a full login as this user
So, how do you log in as root? I'd like to try this so I can just press 'Test Print' to see if this is the issue.