When I select "Hi Peachey" at the top from any location (e.g. forum, someone else's profile, etc.), I get the error page "the page you are looking for doesn't exist."

That's been hapening to me as well -  With my Critterdee.

Still happening? There's a part of our system responsible for this kind of stuff (going to users profiles/posts) and sometimes it has the hiccups.

If not, when you click on the link, what URL is it trying to go to???

It seems to be working now.