Why can't I put notes into my Call log as before?

Why can't I put notes into my Call log as before?

I tried logging a call today, I clicked on log a call  and new pop up appeared. Considering I used this system yesterday a pop up menu didn't show up. I filled in details but when I went to try to edit log a call to put notes in it keeps saying, cannot be processed, and I need to add a new task instead of just clicking save and create new task like before. Please can someone tell me how to put notes in Description box.