I had this problem [[WordPress 2.2.1 broke my site!|when I updated my WordPress to 2.2.1]]: WordPress and K2 stopped talking. Sort of like a bad relationship.
Given, the two products are made by entirely different groups. Sadly, K2 is a bit behind WP at the moment. In fact, K2 breaks my dashboard (I have to manually punch in the URL for writing a new post), and now it seems K2 RC4 has busted my columns, shrank the font size on my tag cloud(??), and renders completely differently in IE than in Firefox.
I might have to change themes until K2 is fixed.