Dashboard Not Complete

Today when trying to post an article, there was no way to add a category either on the dashboard or beneath the category list on the post page.

Also, when I click to publish an article, I get an error page that states that the header cannot be changed… Yet when I click to view the post, the post was published as usual.

I had used WordPress for almost a year now with very few problems. However, they have become must more numerous.
HELP!!!