#2 Dec 13, 2016 07:12
The error is produced by the XHTML validation. Disabling it will let you save your posts as usual. However, it will make your site a bit insecure. You can find more info here: http://b2evolution.net/man/group-properties-blogging
What version of b2evolution are you working with? Why do use CKE editor? Where did you get it? What version?