error/core plugin/detectedmisplacedplugin

DO NOT PANIC THIS IS EASILY FIXED

Let me guess, you arrived here after trying to install a new theme? If so then check that the version.php of the theme in question, and make sure that it is completed correctly, especially this line...

$plugin->component = 'theme_yourthemename'; // Full name of the plugin (used for diagnostics)

...where 'yourthemename' is the correct spelling of the theme you are trying to install.