See reportings in http://forum.piwik.org/read.php?2,78979
When browsing CoreAdminHome a 404 error File does not exist: /home/piwik/public_html/themes/logo.png occurs
This also affects image logo-header.png
The correct uri should be /themes/default/images/logo.png
PHP 5.3 Piwik 1.5.1
Keywords: 404 file does not exist image logo png
It sounds like Piwik believes you have uploaded custom logo but it is not there, maybe you removed it or moved Piwik from one server to another?
I just came across this error on a fresh install (2.14.3)
missing files: misc/user/logo.png and misc/user/favicon.png
on the CoreAdminHome page option "use a custom logo" is set to "no" but in the HTML code hidden
<img> tags try to load these non-existing files. Please integrate the fix from @anonymous-piwik-user - thanks!