My old topic for this got closed. Still an issue so I thought I'd reopen it:
I have External Links installed and running on a theme with P2 installed, and it causes something to break. When I click the reply link on a post, rather than just opening a reply box beneath the post, a little P2 status pop-up appears and says "Log In Again" briefly, then disappears, then redirects me to the unique page for that post, with a reply box. Its not a huge deal, 'cause you can still reply, but its kinda annoying and you don't get the cool in-line reply box.