rtcontrib issue (stuck on p.16 of understanding rtcontrib tutorial)

Having sorted out my Radiance v4.1 installation, i am proceeding along
in AXEL's rtcontrib tutorial and have encountered a bizarre error when
i try to render the 145 + 1 images (p.16) that make up the sky

vwrays -ff $vw | rtcontrib @rtc.opt -ffc \
$(vwrays -d $vw) -V+ -f tregenza.cal -b tbin \
-o images/patches/p%03d.hdr \
-m sky_glow testroom_whitesky.oct

All of the 146 images are about 1.4 MB, but when i try to open them in
Photosphere, i get the following error message :

"Truncated file: unexpected EOF (scanline 597)"

Is there something obvious i am missing here?

It appears that others have successfully worked their way through this
section, so perhaps again it is a setting on my machine.

However, i have SUCCEEDED in generating the 146 images for an interior
view from Andy's 3-phase tutorial (uses many of the same scene files)
as such:

vwrays -ff -vf views/back.vf -x 600 -y 600 | \
rtcontrib `vwrays -vf views/back.vf -x 600 -y 600 -d` -ffc \
-fo -o images/vmx/window_%03d.hdr \
-f cal/klems_int.cal -b kbinS -bn Nkbins -m windowlight \
-ab 2 -ad 1000 -ds .15 -lw 1e-4 model_vmx.oct

Any suggestions would be appreciated !