[Radiance-general] Problem with mesh texture coordinates

[Mark Stock]

I am using a Radiance mesh primitive, converted using obj2mesh, 
which contains texture coordinates. I want to use those texture 
coordinates to set the grey reflectance of the mesh. But when I 
rvu the model, I get:

rvu: Ly`grey: undefined variable

My .obj file looks like:

vt 0 0.136413
v -1.86092 -2.25017 -0.364442
v -1.8692 -2.23265 -0.387964
v -1.8692 -2.22994 -0.385942
v -1.86092 -2.24745 -0.36242
v -1.87395 -2.25237 -0.361491
v -1.88223 -2.23485 -0.385014
v -1.88223 -2.23214 -0.382992
v -1.87395 -2.24965 -0.359469
f 1/1 2/1 3/1
f 1/1 3/1 4/1
f 4/1 3/1 7/1
...

My scene.rad file is:

void brightfunc basecolor 2 refl grey.cal 0 0
basecolor plastic def 0 0 5 1.0 1.0 1.0 0.0 0.0
def mesh amesh 1 scene.msh 0 0

And grey.cal is simply:

refl = Ly;

What am I doing wrong?

Mark