When I run the following command at my command prompt (Linux, bash, LXTermianl):

rfluxmtx -ab 2 -ad 512 -as 256 -dj 1 -dp 1 -dt 0 -dc 1 -lw 0.001  -n 7 -faa -v scene/shades/WG1_SHADE.rad skies/dc_sky.rad -i octrees/model_dc.oct > "output/dc/WG1.dmx"

I get the following error:

rfluxmtx: warning - ignoring output file in sender ('output/dc/WG1.vmx')
rfluxmtx: opening pipe to: rcontrib -fo+ -ab 2 -ad 512 -as 256 -dj 1 -dp 1 -dt 0 -dc 1 -lw 0.001 -n 7 -fda -c 10000 -bn 1 -b 'if(-Dx*0-Dy*0-Dz*1,0,-1)' -m groundglow -f reinhartb.cal -p MF=1,rNx=0,rNy=0,rNz=-1,Ux=0,Uy=1,Uz=0,RHS=+1 -bn Nrbins -b rbin -m skyglow -y 145 '!oconv -f -i octrees/model_dc.oct skies/dc_sky.rad'
rfluxmtx: sampling 145 directions
rcontrib: system - cannot find BSDF file "bsdf/C20.0-W6.000-S2.308-A0.0-V0.50-S0.50-D0.01.xml": No such file or directory

The warning - ignoring output file in sender is OK I think, but not finding the BSDF in the material file confusing. It's in the subdirectory right below and I've also tried moving it to various places, changing the reference in the material file to match the new location. My $RAYPATH and $PATH find everything else fine.