Tags no longer work

After upgrading to 3.5, clicking on a Tag in the Tag cloud or at the end of a post no longer works, ie, a message says “Sorry, no posts matched your criteria.” Obviously, if I go into the Dashboard and then click Tags, I can see them all there along with the number of posts that have each Tag attached. Is this a known-issue, or am I the only one experiencing this since the new version?

Many thanks for any help or advice.