All right, then it likely is indeed that some part of the process–whether YABEE converting the model, or Panda loading it, or the conversion from egg to bam, or something else–is running into that aforementioned memory limitation instated by Windows.
I’ve run into similar effects myself when exporting and loading large levels, but since I’m using Linux the result is instead simply that my computer becomes unresponsive until the process is complete.
In my case I found that it helped to split my level up into “chunks” (managed in Blender by an add-on).
If that’s not feasible in your case, could you perhaps replace part of the level-model with a heightmap, and then add elements unsuited to a heightmap (like overhangs) via separate models?
(As to implementing a heightmapped terrain, Panda’s GeoMipTerrain class may do the job; I’m not sure offhand of whether it’s been superseded, however.)