[OpenLayers-Users] why no overlay on Virtual Earth basemaps?

[Ernie Buford]

Having fun getting started with OpenLayers, but I've hit a curious snag....

I have a set of map tiles created using Arc2Earth, and they overlay 
nicely on Google, Yahoo, and OSM basemap data.... but no luck with 
Bing/Virtual Earth.  Is this not currently possible, or (more likely) am 
I missing some critical detail?

I have modified several OL examples (e.g., 
OL_spherical-mercator-example.html and some from the 2.10 Beginner's 
Guide) by adding an XYZ layer like this:

     // create slope overlay layer
     var slope = new OpenLayers.Layer.XYZ(
         "VT Slope",
"http://myserver/slope/${z}/${x}/${y}.png",
         {
             'opacity': 0.6, visibility: false,
             'isBaseLayer': false,'wrapDateLine': true
         }
     );

At times I've added the 'sphericalMercator: true' option, but it does 
not seem to matter.

I've added this exact chunk of code to several working examples.  The 
slope layer shows up over any of the aforementioned basemaps except Bing 
(which I've tried accessing via OpenLayers.Layer.VirtualEarth as well as 
directly with the newer OpenLayers.Layer.Bing).

Why won't this work with the Bing/VE basemap?

Should I be using a different method for using this type of tile cache 
as an overlay in OL?

Ernie