You are likely using YABEE version below 12 on Blender version 2.63.
Maybe you didn’t overwrite the old script files properly?
In 2.63 BMesh was added which adds ngons support to Blender, but breaks some old code.
Mesh.faces is now Mesh.polygons. Or if you don’t want to modify your script too much there’s Mesh.tessfaces which is there just for backward campatibility. With the latter you only need slight code modifications to make your old scripts work in 2.63.
mesh.update(calc_tessface = True) # so Blender will generate a triangulated copy you can access instead
mesh.faces -> mesh.tessfaces
mesh.vertex_colors -> mesh.tessface_vertex_colors
mesh.uv_textures -> mesh.tessface_uv_textures
I had a Blender script I needed to work on both 2.63 and older versions. Having two separate scripts was too much work as each time I updated one I had to modify the other one too, so I chose to check the version of Blender and access the above data types differently depending on the Blender version.
Maybe YABEE should do that too, it complicates the code a bit but makes it campatible with older Blender versions.
if bpy.app.version == 2 and bpy.app.version >= 63: # for Blender 2.63 API
mesh.update(calc_tessface = True)