I followed the instructions by This

The gcode generated only contains header and footer.

%
(Header)
(Generated by gcodetools from Inkscape.)
(Using default header. To add your own header create file "header" in the output dir.)
M3
(Header end.)
G21 (All units in mm)

(Footer)
M5
G00 X0.0000 Y0.0000
M2
(Using default footer. To add your own footer create file "footer" in the output dir.)
(end)
%

Why am I not able to generate a proper Gcode?

Normally, you select your path, then go into the GCodeTools Extension and tell it to create Orientation Points, Then select a Tool, Then select Path to GCode.  However, if you do nothing but select Path to GCode it will create the Orientation Points for you and choose the Default Tool.  It should work.  If you use the Node Editor can you manipulate individual points?  Did you load a DXF File, or autotrace a bitmap image?

Try drawing a simple square, then select Object to Path.  Try running the Tool on that.