I have 3 WordPress sites on the same server and all are having the same issue. I get an error 500 or HTTP Error when attempting to upload images. This doesn't happen on all images but it does happen on about 75% of images. I know that the easy answer is "There's something wrong with your images." but I've tried converting them to different formats and it doesn't help. I've disabled all plugins, tried installing the ajax-thumbnail-rebuild plugin, edited the .htaccess with every option I could find in the forums and edited the php.ini file. This happens regardless of OS or browser, with or without flash etc. I've checked ownership of wp-content/uploads folder and set it's permissions to 777(for testing), I've verified that I'm running php5 as well. This is driving me nuts and I can't figure it out. I have full access/control over the server. I set the server up using ISPConfig on Ubuntu 12.04.