Yes, I did see this it is probably a wordpress plugin that is creating a javascript conflict in the admin area, try disabling plugins one at a time until you find the one that is creating the problem.

Start with older plugins that you may not be using...

I only use xml site map and all in one seo pack. I disabled both and the same thing happened even after clearing all cookies. I search Google and I am overwhelmed on the number of people having the same problem at wordpress forum. I think I need to wait for their final solution.

Try changing your theme/ use one of the recent WordPress default themes see if that fixes it.

I just solved the problem after updating/disabling/re-enabling all plugins.