We deleted the ThickBox folder in the WP-content folder. This fixed it, but caused a new error with the add link button not working on the main page. Maybe it had something to do with it. Still no sure, let me know if you find a better solution.
Same issue here, today upgraded WP to v3.6 and I can’t edit anything. TB_load box pops up, animates in an infinite loop, I can click outside, but click on any link result again with TB_load box and infinite animation loop.
I have installed *only* Yootheme Radiance and their Widgetkit module, nothing else. (It’s a fresh WP in development).