Ideally, you would need to click on the specific error relevant to the issue and copy the message to paste here. A likely one could be:
NoMethodError (undefined method `enable_personal_messages?' for SiteSetting:Class) app/serializers/topic_view_details_serializer.rb:127:in `include_can_invite_to?' (eval):11:in `_fast_attributes' lib/
Though if you have any third-party plugins that affect PMs then that would be a probable place to start. As Pfaffman says, sometimes safe mode isn’t enough and you would have to remove the plugin from your app.yml and rebuild. What plugins do you have on your site?