I've searched the KB and cannot find anything new beyond these two TID's:

TID10018652 (last modified 08FEB2002)
TID10089461 (last modified 09DEC2003)

My situation appears to be that of the second of these--I run about 200 XP
machines, and one machine will, at random, suddenly stop working w/respect
to web browser. All the rest are fine, but there is NO APPARENT FIX for
the afflicted machine. The user can use any other machine, no problem.
Any user who attempts to use this machine, out of luck. clntrust (v. 1.5)
and dwntrust (v. 1.1) are both being launched from the login script (i.e.
no local copies), so if the file were corrupt it should be corrupt for all.
I had one machine with this problem and have never (in about two months of
trying) been able to get it to work. Authentication is fine, Groupwise is
fine, can ping proxy, all is well, but web access is dead. Am just now
reinstalling an existing machine, using the actual XP Pro disk rather than
an image (thought it might be a problem in the reference machine), and when
I get to the point at which I'm configuring the proxy, I can't get out to
the web. Not hardware, naturally, since it's the same hardware that had a
web connection yesterday. Also, if I point the default gateway at the
actual router, I get web just fine.

Back in 2003, the TID said, "The client group is working on this." I'd
LOVE to know what they came up with...?