On the 23.Jan. 2011 I upgraded to JOSM 3751 and had the same symptoms:
***Red error tiles overlaying the Bing imagery.***
*NOTE: I am using a German version of JOSM so the following word translations to English could well be wrong!*
I went to "Einstellungen" i.e. F12 (Perhaps "Setup" in English)
- pressed the WMS TMS button to go to "Einstellungen für Hintergrungebene" Hintergrundebene" (Setup for Backgroud levels)
- The list of "Bilddienste" (Picture Services/Providers) was:
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Bing Sat bing:bing
Bing Sat bing:bing?
LandSat wms:http://onearth.jpl.nasa.gov/wms.cgi?request=GetMap&layers=global_mosaic&styles=&format=image/jpeg&
LandSat wms:http://onearth.jpl.nasa.gov/wms.cgi?request=GetMap&layers=global_mosaic&styles=&srs=EPSG:4326&format=image/jpeg
Landsat (Spiegelserver) wms:http://irs.gis-lab.info/?layers=landsat&
OpenAerial-Karte wms:http://openaerialmap.org/wms/?
VERSION=1.0&request=GetMap&layers=world&styles=&srs=EPSG:4326&format=image/jpeg
OpenStreetMap tms:http://tile.openstreetmap.org/
Yahoo Sat html:http://josm.openstreetmap.de/wmsplugin/YahooDirect.html? -
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As I could not see the point of the second line **Bing:Bing?** I elimated it and after a JOSM restart Bing imagery worked perfectly!