There's an issue over in the CSS Injector queue that has been tracked to a bug with the WYSIWYG module. The CSS Injector module uses the public:// protocol for its CSS files. When used on pages with a WYSIWYG module, the WYSIWYG textarea tries to call the .css file as well, and fails - leading to a bunch of watchdog errors.
The fix it to add support for the public:// protocol in the wysiwyg_get_css() function.
Patch coming in first comment...