What user are you running spamd as?
If you are running it as root (so that users can control their options
themselves) then you'll need to do 2 things.
1. create the .spamassassin directory for root so that it can lock files
etc (I'm actually not totally sure this is nessessary but I did it an
I don't think using -c and -x means much. You are disabling per user
config files with -x but wanting to create them if they don't exist.
Using -a in this case you will get a site-wide auto-whitelist, your
error is occuring because the user id of spamd doesn't have write
permissions where it'