For all of you having trouble accessing the input fields for the latest release of this plugin running the latest release of WordPress, here's a quick fix on how to revert to the previous version, which will provide you with all the functionality again.
1 - Navigate to Plugins >> Deactivate HeadSpace2 SEO
2 - Delete HeadSpace2 SEO
3 - Go to http://wordpress.org/extend/plugins/headspace2/download/ and download version 3.6.38 (zip)
4 - Navigate to Plugins >> Add New >> Upload
5 - Upload the zip and press the Install Now button
6 - Activate your old version of HeadSpace2 SEO and enjoy all the functionality again =)