I have the same problem after upgrading to Pro 4.2.6. It doesn't seem to perform as well and now I can't even connect to any ultrapeers despite trying all of the suggestions posted here, including deleting the LW prefs folder.

I'm running on XP Prof, behind a Sonicwall firewall, connected by an ethernet cable to a LAN at work, 448 RAM and 14 gigs of HD space.

Any other ideas?