I have checked the issue and tried to resolve it myself. The issue is the plugin internally uses wp-api for getting the form to be displayed for preview but it is not compatible (from plugin version .0) with the older version of WordPress. Thus either update your wordpress otherwise use the version earlier you were using.
Also in the minor versions of the plugin there are some major changes. I tried using the latest minor version but the Manage Forms button was having problems. Thus i had to use the exact same version i was using earlier.
