Im getting this error everytime I click on a left nav option in the newsletters section. eg. 'Drafts', Sent Items' etc

Fatal error: Argument 1 passed to TabSet::push() must be an instance of Tab, called in /home/www/web11/web/elmswood/sapphire/forms/FieldSet.php on line 52 and defined in /home/www/web11/web/elmswood/sapphire/forms/TabSet.php on line 71

I was having trouble with the newsletter signup form not adding the details to the database, so i just upgraded to 2.1.0rc1 to see if that would fix it. The form is submitting and submitted details are showing up under the 'Submissions' tab in the 'Site Content' area, but nothing is showing up in the 'Newsletters' area and im now getting these errors.

Please let me know if you need any more info

Yep, me too... not sure if something must be set up initially before this to work, but giving a fatal error is never a good thing

Experiencing this in SS2.1 rc1 and in SS2.1 stable version.