I've had the same problems.. I would manually change chmod to 666 on the db files then a day or so later they would changed back to 644.. I found out that my host has a cron tab chowning files to 644...This could be your problem as well.. all I did to fix this was add chmod code in the privsend, privread etc files...so each time a user uses the pm feature it will update the files being used.. good luck
