Our environment currently contains a hybrid of 2003 and 2007 exchange and
clients. We recently posted a network install of 2007 client in an attempt
to let users voluntarily upgrade whether they are on 2007 exchange or not.
As users continue to upgrade about 20% of them are not able to connect to
exchange after the upgrade. I have done extensive troubleshooting in
addition to having an MS case open for 2 weeks with no luck. It doesn't
matter what version of exchange the users are on as its definitely a profile
issue as creating a new windows profile for the users solves the issue. I
would like to have a better fix as doing this for remote users is tedious.
We have tried all obvious things like, rename outlook folders, deleting ost,
cache mode non- case mode, trying resolving to global catalog server
instead, reinstalling 2007.

Also worth noting is that rolling back to 2003 client works as well so there
is something in the profile for only certain users that is getting corrupt