Admin: Error message when trying to expand categories

In the admin part in the categories page I try to expand the categories by pressing on the “+” icon.

However, instead of the categories being expanded I get this error message in Firefox.

In Chrome nothing happens and it keeps waiting.

I haven’t done any modification on the admin pages. I just upgraded to 2.1, but I don’t use this feature often so it might have existed earlier.

I want to delete some subcategories. Any ideas for a fix or a workaround?


Seems fixed in 2.1.1 (minus some visual nits). Thanks guys!