G02 problem

Hi all. This is my first post to this group, however I have listened
in for quit some time. I just finished my first cnc router table and
have been playing alot. I am using gecko drives and master5 (demo for
now still deciding) everything is working well and tolerances on
linear cuts are precise enough for my needs. I am however having a
problem when I run a G02 or G03 command. The machine also wants to do
helical instead of circular, in that as it is cutting the arc it
moves the z axis up or down depending on the arc direction. I checked
that the defalt plane was x,y in master5 and have looked for help in
an old cnc programming book I have, but nothing yet. Was wondering if
anyone could spare a moment to help a new member. I am sorry for the
very basic question but it seems as though this is by far the best
place to learn from.

Thanks
Dan