Unable to add content

Hello all,

I am unable to add content to http://www.musicofarmenia.com‘s certain sections – it started with the events and videos section (we have no disabled the events section)
but today I discovered, I am also unable to add content to the music section.
We are still able to add content to the news and musicians section and to the two windows and the banners on the home page.

Can you please tell me what might have gone wrong?

Drupal version: 

Source: https://www.drupal.org/taxonomy/term/22/feed