The most likely issue when you cannot connect is a conflict with another plugin installed on your site. We keep a running list (below) of WordPress plugins that can break your site.
If you are using any of these plugins, please try the steps indicated next to the plugin.
- CloudFare (disable the setting “https protocol rewriting” and it should work)
- Killabot APx: http://www.killabot.net/?p=153
- Mofuse: http://www.mofuse.com/
- Resize At Upload Plus: http://wordpress.org/extend/plugins/resize-at-upload-plus/
- WP Captcha Free - disable the plugin to login to the WordPress App
- WPBook - disable the plugin to login to the WordPress App
- WPIDS - disable the plugin to login to the WordPress App
- Bad Behavior - disable the plugin to login to the WordPress App
- Role Scoper - disable the plugin to login to the WordPress App
- WordPress Tiniest Super Cache - disable the plugin to login to the WordPress App
- WP HTTP Compression: http://wordpress.org/plugins/wp-http-compression/
- WordFence - Can block XML-RPC requests (Version 5.0.3 of WordFence works with the app)
- CLEFT - You can disable CLEFT, then login to the WordPress App and re-enable CLEFT.