Are you getting this with 2.0.2? I changed it to use wp_mkdir_p() instead. It shouldn’t be complaining that the folder exists since I only run this function when it doesn’t, but it may be a more subtle issue than that. Can you verify if it works when you create a “wp-content/uploads/crayon-syntax-highlighter” directory with chmod 774 or 777 or similar? That shouldn’t pose any threats since all you’ll have in this directory are css themes, but try to use something other than 777 🙂 If that works then it’s clearly a permissions issue. I’ll use a @ to hide the error and log it in log.txt in any case.