The same error?
Go into your hosting file manager and go to wp-content/plugins and rename the gp-premium folder to something else. This will deactivate the plugin.
The initial error you gave me is just a PHP warning which wouldn’t take the site down.
I’m running this new version on multiple different hosts (including this site) with no issues.
Can you contact your hosting and make sure your server is using a fairly recent version of PHP?
If you’d like to email me ftp details to firstname.lastname@example.org I can look into this for you?