I'm sorry that you're having trouble with permissions and apologize for the frustration I'm sure this may have caused. We have been moving users between groups, using an "automatic promotion" to separate long-time, trusted users like yourself from brand new registrations (in order to combat the link spam that you've noticed).
However, you are in the advanced group and should be allowed to do most of the expected actions, including replies and access to almost all areas of the site. I've just taken a look at the permissions for that group and it really looks like you should be able to do this.
If you logout and back in, does that fix the issue? Otherwise, can you outline a course of action that results in an unexpected "permission denied error" so we can test from our offices?
Thank you for your cooperation.
Any reason I don't have permission to access pages or reply?