Regarding my previous post - SOLVED!
The uid was not unique! I had used a uid=4 as it was my fourth entry in my custom onlinemapsources.xml file. However, the standard onlinemapsources.xml file has a uid=4 used by OpenStreetmap Mapnik. When I changed the uid to a unique number, in this case uid=5, this new online mapsource now works with no problems.
The uid was not unique! I had used a uid=4 as it was my fourth entry in my custom onlinemapsources.xml file. However, the standard onlinemapsources.xml file has a uid=4 used by OpenStreetmap Mapnik. When I changed the uid to a unique number, in this case uid=5, this new online mapsource now works with no problems.