[Radiance-general] rtrace error message "only single process supported"

[Kaori Oyamada]

Hello all,
I tried to use rtrace -n option like below, but returned error message was
"only single process supported". Why can I use parallel calculation?

rtrace -I -h -dp 2048 -ar 32 -ms 0.063 -ds .2 -dt .05 -dc .75 -dr 3 -n 2
-st .01 -ab 5 -aa .1 -ad 2048 -as 256 -av 0.01 0.01 0.01 -lr 12 -lw .0005
 -af ***.amb ***.oct < ***.pts > ***.dat

My computer specs are
OS:Windows XP professional SP3
CPU:core 2 duo T9300  2.5Ghz ( I command rtrace -n 2 )
Memory : 3GB
Radiance windows binaries are downloaded from here.
http://openstudio.nrel.gov/getting-started-developer/getting-started-radiance

Thank you for all your advice.
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