Error in inkscape extension while making gcodes

I have installed the inkscape 0.92 version and added a cnc plotter extension to it's path and i am getting this error again and again with old versions too. With the inkscape i am trying to make gcode files.

 I followed these steps first i import a image and then select trace bitmap option from there i select brightness..... and click on update and then ok. Now i removed the original image and select the vector image formed now i use the extension to generate a gcode file but this error shows up.

Error-
Inkscape has received additional data from the script executed. The script did not return an error, but this may indicate the results will not be as expected.

In text box-

Traceback (most recent call last):
File "C:\Program Files (x86)\Inkscape\share\extensions \servo.py", line 3172, in <module>
e.affect()
File "C:\Program Files (x86)\Inkscape\share\ extensions \inkex.py", line 207, in affect
self.effect()
File "C:\Program Files (x86)\Inkscape\share\extensions \servo.py", line 3156, in effect
self.orientation( self.layers[min(0,len(self.layers)-1)] ) File "C:\Program Files (x86)\Inkscape\ share\ extensions \servo.py", line 3085, in orientation
doc_height = self.unittou-b(self.document.getroot0.xpath ('@height', namespaces=inkex.NSS)[0])
AttributeError: laser_gcode instance has no attribute 'unittouu'

This was the error with first extension
When i tried another extension the following error appears.

Inkscape has received additional data from the script executed. The script did not return an error, but this may indicate the results will not be as expected.

Traceback (most recent call last):
  File "servo.py", line 3172, in <module>
    e.affect()
  File "C:\Program Files\Inkscape\share\extensions\inkex.py", line 283, in affect
    self.effect()
  File "servo.py", line 3156, in effect
    self.orientation( self.layers[min(0,len(self.layers)-1)] )
  File "servo.py", line 3085, in orientation
    doc_height = inkex.unittouu(self.document.getroot().get('height'))
AttributeError: 'module' object has no attribute 'unittouu'

please help me to resolve the problem.