Navigating to a virtual page on the website I get the following error:

[Notice] Trying to get property of non-object
GET /about-us-v/?stage=Stage
Line 151 in xxx/www/sapphire/core/model/VirtualPage.php

Possible solution:
In core/model/VirtualPage.php - method init():

if($this->record->ID){ ...

$this->record is as far as I see not a property of class VirtualPage. Possible replacement (I'm not sure, but this seems to do the job):

if($this->dataRecord->ID){ ...

Also in the init() method:

$this->VersionID = $this->failover->CopyContentFrom()->VersionID;

It looks like VersionID is not part of the properties returned by $this->failover->CopyContentFrom(). Possible replacement (seems to be working as well):

$this->VersionID = $this->failover->CopyContentFrom()->Version;

(question: it looks like $this->failover in this case refers to $this->dataRecord as well. Or am I mistaken - still trying to figure out the stucture of the code here)

I get the same error in 2.3.0 rc2:

[Notice] Trying to get property of non-object
GET /forschung-31/
Line 150 in /srv/www/ss_sec/silverstripe-v2.3.0-rc2/sapphire/core/model/VirtualPage.php
Source
141     }
142     
143     /**
144      * When the virtualpage is loaded, check to see if the versions are the same
145      * if not, reload the content.
146      * NOTE: Virtual page must have a container object of subclass of sitetree.
147      * We can't load the content without an ID or record to copy it from.
148      */
149     function init(){
150             if($this->record->ID){
151                     if($this->record->VersionID != $this->failover->CopyContentFrom()->Version){
152                             $this->reloadContent();
153                             $this->VersionID = $this->failover->CopyContentFrom()->VersionID;
154                     }
155             }
156             parent::init();

Trace
VirtualPage_Controller->init() 
 Line 113 of Controller.php
Controller->handleRequest(HTTPRequest) 
 Line 19 of ModelAsController.php
ModelAsController->handleRequest(HTTPRequest) 
 Line 257 of Director.php
Director::handleRequest(HTTPRequest,Session) 
 Line 106 of Director.php
Director::direct(forschung-31/) 
 Line 111 of main.php