Well after finding this out the fun ( read that as a lot of digging in the code ) way I found the same solution as mentioned here by a few others.
But the clients site had a bucket load of plugins so I had to hunt down the offending one.
So ichurakov, jeffduyndam and SocialMediaCop.com have the answer.
The Culprit is version 2.0 of the plugin.
The reason this goes BANG! is because wp_admin_css will echo the CSS link immediately and this is being done inside the constructor which is instantiated in popup-domination.php.
So I’m guessing that WP runs all the active plugins prior to doing all its other bits and pieces… basically what the guys have done is naughty!
You’ll see in the browsers source code, on the pages that show the errors, the CSS link having been sent out prior to the rest of the page being rendered and of course prior to WP doing all its other bits it needs to do. Like headers and cookies etc..
The CSS file being called doesn’t even exist in WP > 3.3.x so there is no harm in clobbering it ( whoops – commenting it out ).
So there’s a trap for plugin writers…
Cheers!
