this may be because it cutted only the 1st pass on the thread, thus a single G32 will only go once towards Z-
to cut the thread, you need all G32s, and in each one you may need both x&z
so :
Code:(01156.MIN) N10 G50 S2000 N11 G0 X400. N12 G0 Z400. (THREAD1) N13 T020202 N14 M8 N15 G94 N16 G97 S500 M3 M41 N17 G0 X2.8 Z0.1969 N18 G0 Z0.3181 N19 G1 X1.9496 F39.3701 N20 G32 X1.9496 Z-1.2431 F0.0787 N21 X2.065 Z-1.3009 F0.0787 N22 G0 X2.8 N23 Z0.3181 N24 G1 X1.9311 F39.3701 N25 G32 X1.9311 Z-1.2339 F0.0787 N26 X2.065 Z-1.3009 F0.0787 N27 G0 X2.8 N28 Z0.3181 N29 G1 X1.9168 F39.3701 N30 G32 X1.9168 Z-1.2268 F0.0787 N31 X2.065 Z-1.3009 F0.0787 N32 G0 X2.8 N33 Z0.3181 N34 G1 X1.9049 F39.3701 N35 G32 X1.9049 Z-1.2208 F0.0787 N36 X2.065 Z-1.3009 F0.0787 N37 G0 X2.8 N38 Z0.3181 N39 G1 X1.8943 F39.3701 N40 G32 X1.8943 Z-1.2155 F0.0787 N41 X2.065 Z-1.3009 F0.0787 N42 G0 X2.8 N43 Z0.3181 N44 G1 X1.8943 F39.3701 N45 G32 X1.8943 Z-1.2155 F0.0787 N46 X2.065 Z-1.3009 F0.0787 N47 G0 X2.8 N48 Z0.1969 N49 M9 N50 G90 G0 X400. Z400. N51 M2
also, like mr wizard said, try G33 instead of G32, and all stuff from post #14