It could be something with your Wordpress installation; specifically the plug-ins your using.
Attempt to disable all your Wordpress plug-ins and then attempt to post, if it works, there's a plug-in that's causing the problem. Re-enable the plug-ins one by one, trying each time to post, repeat the process until you've found the problem plug-in.
Just trying to help...
-------------
Later,
LEHenryJr.