[Plugin: PC Custom CSS] 404 errors due to pc custom css

I am getting url 404 errors due to this plugin, though the plugin features are working correctly.

e.g.
example.com/wp-content/plugins/pc-custom-css/custom.css?pc_custom_css_ver=1332436296

is showing up in error logs

Any ideas why?

http://wordpress.org/extend/plugins/pc-custom-css/