OK, I'm on my Win 7 machine, and not getting errors.
What I did was log out. I received the "cookies cleared" messaged, then shut down all instances of TS I had open.
I surfed the forums, (not logged in), and attempted to access about 50 threads, in different categories, all successfully.
Previously, I had been receiving this error only at the individual thread level, either attempting to access a thread, or attempting to submit a reply. The denial of access was somewhat random. In other words, I could access the same thread, or be denied access at different times.
Ironically, it was this thread that was giving me the most trouble....
Makes me wonder if the cookie was corrupt. Just a wild guess from someone who has no idea what he's talking about.
I should add that the only scripts I have approved are Techspot, and Googleapis.