It seems that I still have a problem with the biped_auto_rig, in that when the script is done I have no skin to work with.
I dive down into the skin network and set the File__source from_file sop to my geometry only to develop an error at the rightside group sop.
I mentioned the problem here http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=9696 [sidefx.com]
I also noticed that the mirrorgroup group sop has the same expression, which if it worked would give the rightside and the mirrorgroup the same points. Right?
I am now using version 9.0.734 win64
on a previous version 9.0.727 I tried both the 32 and 64 bit version and got the same problem.
I even tried the expression with a box set to polygon mesh with the same results.
Here is a screen shot of the error report (MMB on rightside sop).

I'm really not sure what is causing the problem with the group expression. If you wouldn't mind sending me the otl and geometry file I can try and track the problem down.

As for the right side and mirror group, they differ in that one is a point group and the other is primitives. Upon closer analysis they actually appear to have their names switched.

Actually never mind. Since you were nice enough to post a screenshot I can tell you that the problem is that the node has its script language set to Python. I'm guessing you have your default expression language set to Python. Changing it to Hscript will fix that.

Alternatively, you could replace $TX < 0 with
pwd().curPoint().position() < 0 so it would work with python.

I'll look at adding a check for node language so this doesn't happen again.

Thank you your solution worked purfectly, but to insure that I did not have to worry about that problem again I changed to hscript in preferences.
Now to try my hand at animation. after I finish the rigging.

This is fixed in tomorrows build.

When creating a deform rig, we now specifically set the group sops as well as the rop output drivers expression language to be Hscript.