Make sure your WordPress plugins are up-to-date
This is probably stating the obvious, but make sure your plugins in WordPress are up-to-date. You keep up with the latest WordPress releases (and you should — there are lots of security fixes within releases), but you also have to make sure that the plugins are updated.
I deploy some systems using SVN, and on some sites, make use of the Disqus plugin for commenting. The plugin itself, as of writing, has only been tested against WordPress 3.1.4. Today, you have WordPress 3.2.1. Don’t fret though — Version 2.66 works just fine.
Upon a little search later for wordpress 3.2.1 upload image, I see a bunch of people asking questions. The standard answer is to disable plugins to see if things work. In this case, updating solved the problem.