Unknown: Cannot use output buffering in output buffering display handlers in Unk

If you temporarily deactivate all other plugins and / or switch to the twentytwelve theme does the problem go away?

yes if i dasable all the plugins the problem go away i need to discover what plugin is causing this, other thing i have noticed is this in the html page code:

Status: not cached

but the cache is enabled

Ok, so you can re-activate other plugins one-by-one until it breaks again and then there’s something to investigate.

I get the same error when I enable any part of W3TC (page caching, DB caching, etc.). The problem only appears when downloading an MP3 using our download plugin. When someone downloads an MP3, the resulting file does not contain MP3 data but the following text:

<br />
<b>Fatal error</b>:  Unknown: Cannot use output buffering in output buffering display handlers in <b>Unknown</b> on line <b>0</b><br />

Here’s the crucial snippet from our download plugin. Is there any way to disable caching for pages served by this plugin. It’s keyed to a trailing “folder” on the url called “/download-audio”

header("Pragma: public");
			header("Expires: 0");
			header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
			header( "Cache-Control: private", false);
			header("Content-Type: application/force-download");
			header("Content-Type: application/octet-stream");
			header("Content-Type: application/download");
			header('Content-Disposition: attachment; filename="'.$file_name.'";');
			header("Content-Transfer-Encoding: binary");
			$filesize = filesize($full_filename);
			if ($filesize != 0)
				header("Content-Length: ".$filesize);
			ob_clean();
    		flush();
			readfile($full_filename);
			exit;

Almost forgot:
Wordpress 3.5.1
W3TC 0.9.2.11

Hi, Can someone please help?

I have created a site on a temporary space and have now moved it to the correct location however all of the internal pages are now showing a 500 error? The home page and admin area work fine. i have tried trouble shoot and have done the below

1. check phpmyadmin to make sure the right domain is set
2. reloaded wp-includes and wp-admin from fresh WP install
3. deactivated all plugins and re activated them
4. activated another theme (same issue occurs)

I’m lost! The domain name is https://hardcastlesocialmedia.com.au/ any help would be appreciated.

Thanks

his erros happens when i activate the minify, when i dasable the minify it stops, someone knows how to fix this?

Thanks to the above comment, I investigated our W3 Total Cache plugin minify settings. All I did was go to this line; To rebuild the minify cache use the [empty cache] operation and clear the cache.

That fixed it for me.