This does happen sometime. Usually, logging out of the course and then logging back in will take care of this problem....
By default feedback activity is not enable in the site. To enable it, go to Settings > Site administration > Plugins > Avtivity modules > Manage activities and click on the show icon ( ) to enable it....
As an administrator, go to Settings > Site administration > Plugins > Activity Modules > Feedback. Change "Allow full anonymous" to yes. Then click on "Save changes" button. ...