vizzitor

Thanks a lot brendymullan! I would have never found it!
I removed and it works fine now!

And brendymullan, if you change back from the safe theme to your own theme the message reappears again, or is it gone forever?

This is how it looks like:
https://www.pto.hu/post/1/2520
it also changed my background

Fortunately I can access the admin at least.

I am using a custom modified theme, not sure what was the original. But I am using it for months with no problem.

The plugins I have installed.
Which ones do we have in common?

Add image_src Meta Tag (this was added lately)
Akismet
fbLikeButton
Google XML Sitemaps
SEO Ultimate
Tumblr Widget
W3 Total Cache
WP-PageNavi

I am trying to turn off all the plugins first.

Have you found the solution? It happened to me also this evening. I did not updated the engine, did not do anything but the same message appeared. But there is no .maintenance file to delete nor can I find any of the text or code in the files, I even deep searched for the HEX value of new grey background color it set but no hits.
PLS Heeeeeelp. have you found the solution?