Hi
I have just added a collection to an existing b2evo installation, prior to which it had three collections, mostly manual type.
On setting up this fourth one I chose the Experimental (Green Bootstrap Theme) which as an off topic has a pretty horrible pale green background.

Once created with no demo or other content I made a category. So the collection now has the default [Uncategorised] and my new one which in this case is [tronics]

Now the front page is fine but once I click on the new category I see this warning as in the screen shot, it also occurs when I click n the default [uncategorised] so was probably an issue before I created the new category.

Requested widget container chapter_main_area does not exist for current collection #12 and skin type normal!

I will investigate further, so this is more a discussion than an urgent request for support.
Thanks