G2 G3 Not interpolating correctly

I'm trying to set up my lathe. Up to now most things are working fine, however, when programming a radius the tool plot screen shows the desired tool path, but the actual tool cutting path is simply a straight line joining the start and end points like a chamfer. Below is a sample of code.

G0X3.Z2.
G1Z0.F0.1
X4.
G3X24.Z-10.R10.
G1Z-15.
G0X30.
X80.Z50

What do I need to look for? Is it a configuration error ?

Nick..

I've found it.
For some reason it keeps reverting back to G17 even though I have G18 in my start up code (.ini file)