[drupal-devel] access denied while logged with uid = 1

I have a drupal 4.6 serving multiple sites. Some random problems are arising eventually. 1. php out of memory. i allway had 8m for php execution, now sometimes php cries, is this normal. 2. sometime I get access denied even while logged as admin (uid = 1). For example, I can list the access control table /admin/access, but if i change something and save permissions, i got an access denied. Then, while the path is still /admin/access i can't relogin, i should manually point the url to / and the login. Any advise/workaround for at least manage access control is welcome. Regards, maykel