While activating the plugin, if you come across error message "Plugin does not have a valid header", Please follow the below url which has a fix for this problem. If this does not solve the issue, kindly contact us with login and server details of the website so we can look into the issue further.
https://scotty-t.com/2011/03/28/fix-for-the-plugin-does-not-have-a-valid-header/