vrpn error, PPT is connecting
 

I can't figure out where I should be looking to fix this.
I'm having a problem with one particular script, but others that track head and hand are working fine which leads me to believe that someting may have been inadvertantly changed in the script since last time I ran it (when it also was working fine).
I'm getting an error about being unable to open a serial port, but PPT is connecting. Full error message below.
Thanks!

vrpn_open_commport: cannot open serial port: No such file or directory
Traceback (most recent call last):
File "C:\Program Files\WorldViz\Vizard30/python\viz.py", line 8043, in __update
** NOTIFTY: Connected to PPT on COM4
if not self.nextAction(pool,overtime):
File "C:\Program Files\WorldViz\Vizard30/python\viz.py", line 8095, in nextAction
newAction.begin(newAction._obj_)
File "C:\Program Files\WorldViz\Vizard30/python\vizact.py", line 1227, in begin
self.meth(*self.args,**kw)
File "DE.py", line 155, in begin
tracker = tracking.track_hand_and_head( hand, 'didactic' )
File "tracking.py", line 30, in __init__
self.loaded_ppts.append( ppt )
AttributeError: track_hand_and_head instance has no attribute 'loaded_ppts'

never mind, figured it out.
thanks.