There was a issue with older versions like yours. Depends on what feature was used to generate the error but I recall it was a simple fix that a field was missing on the form tags.
If the error occurs on just browsing the forums not posting something. You may want to open a support ticket.
As far as the config file going to 0 bytes. I would suppect that is a issue with your host provider. So you may want to keep a current backup to re-upload if it happens again.
