cURL error 28

I decided to try this plugin. After installing the plugin, when I check the site status in Gravity Forms, it reports a cURL error 28. If I deactivate that plugin, the error goes away. If I activate it again, the error comes back. Has anyone else received this error? (Note: It will not appear as a notification. You need to be able to find the error through a status page such as the one that Gravity Forms provides.)