I think there was somthing like a " or ' or ´ ...
The Snippet of LogPageNotFound reads the file and displays it's contents...
I used the Snippet as a dashboard widget, and there must be sometimes a special char that brakes the site.
After enough clicks there where a lot of other 404 - so the special char is no longer displayed by the snippet and the manager works again....
Later some requests again an old url with a special char the plugin writes it in the log and the snippet reads it and writes it direct in the output and brakes the page. Adding htmlspecialchars solved that.
It's definitely fixed now. Tested that a lot.
Big Thanks to mike for his question that helped a lot.
