Plan-G is showing the following:
MapQuest Developer
As of july 11, direct tile access has been discontinued
Looking at the MapQuest plans my guess is that it will no longer be possible for Mr. Arnot to offer Plan-G by donation if he continues to use MapQuest. So it looks like it is now necessary for Plan-G to use OpenStreetMap (as it says on the home page) instead of MapQuest.
Mehr hier:
http://www.tasoftware.co.uk/forum/index.php?topic=3486.0
Temp. Lösung:
Unter Optionen, Kartenprovider auf OpenStreetMap switchen:)