Help----Permission problems

I have a dedicated server on a rack with fasthosts running sql, mysql and

access. My main database is access. I have just had a new section built to my

site that uses sql. The problem is that ever now and then (sometimes twice a

day sometimes twice a week) the site demands a username and password from new

visitors.

When I look at the server the permissions seem to have disappeared and I

have to reapply permissions across the server.

This is having serious consequences on my site which is regularly used. The

problem has only started happening since I had the new site section built and

sql installed. The sql is a shared version available though the hosts. I have

no idea what is causing the permissions problem and wondered if anyone had

any suggestions.