I've had the same problem with IB2.3 here as well for the past 2 months or so.
When viewing a thread with IB you get a response:
Bad Request
Your browser sent a request that this server could not understand.
Size of a request header field exceeds server limit.
Never looked into it further as I figured it was maybe something I'd messed up without knowing.
So having to post this using Voyager 3 :-x
If you find the solution to fixing whatever's causing the problem, can you let me know??