SVT: I took your suggestion and deleted ALL my cookies, and checked it out to make sure that ALL cookies were gone and it didn't work.
However it made me look at the bookmark I was using to get to the particular forum I usually go to. In the upgrade they changed all the separate forum URLs so my old bookmark gave me the 404 error. I should have been more specific in my statement of the problem. I was using my usual link to a particular forum, not the home page of the forums. So, of course, cookies would have no bearing at all on my ability to connect. Didn't think it through.
Thanks to everyone who replied.