After doing an XP repair install, I started getting this error:

microsoft feeds synchronization has encountered a problem and needs to close. We are sorry for the inconvenience.

I eventually found the cause:

IE 7 / IE8 had an RSS feed setup… poor old IE6 (after the “downgrade”), probably didn’t know how to handle feeds.

I found that the problem tends to go away after re-upgrading to IE8 again… but sometimes this doesn’t work.

In those cases, this is what you do:

Start IE8, go to tools -> Internet Options -> Content -> Feeds -> Settings -> untick all the boxes

If you want to start using feeds again, just remember to re-tick the boxes again.