Hi Saguaros,
Sorry to be late in my reply but I have been out of my office for a week.
I do not see the messages you are talking about. When I log in in the backend, nothing is wrong.
Therefore, I made some tests for you.
If you check the page I highlighted in the first message. These messages mention Gavick Template.
The errors are displayed when calling a module named 'Article Footer for a Nature Photography Chronicle'.
It uses the mainbody_bottom position. It is displayed after the content of the article.
When I disable the module, no messages are displayed.
When I enable it, the two messages are displayed.
I did the test on all the pages with a bottom displayed using a module. The errors are always displayed.
So, my thought is that the problem is coming from the template not from another extension or the core.
I hope it will help you to understand the nature of the issue.
Let me know if you want further information.
Sincerely