I upgraded to WordPress 3.6 the other day and immediately got the flowing error:
“error 3.6 blockUI requires jQuery v1.2.3 or later!”
Actually, that’s not the exact error I got, the exact error included version numbers of the current and the required versions. The odd thing being the current version was higher than the required version, but computers (and how they read numbers vs strings) got it all wrong.
I have a ton of plugins installed and took a stab in the dark at sidebar login (it’s one of the few that I use across multiple sites).
It was updating this plugin (for me) that resolved the issue