I am having the same problem except I cannot even log in to my dashboard to deactivate it.
I clicked on activate for the Headspace plugin and now every time I try to log into my dashboard I get a blank page with just this on it:
Fatal error: Call to undefined function add_meta_box() in /home/content/30/4445630/html/wp-content/plugins/headspace2/headspace.php on line 513
Please help!
