Very strange occurence.
I installed a new blog (with the latest 2.1.3) within a sub-directory of an existing account. I have other 2.1.3 blogs - in this same account - that work fine.
With the new blog ... when I click on the widgets (the little three line icon on the right) to edit the widget (as in a text or RSS widget) they will not open and let me edit the widget.
All other blogs at this site have widgets installed and they work fine. Easy to edit.
I've never had anything like this before.