You ran some other code that called G18 and put you in the XZ plane, and didn't return to the XY plane.
MDI G17, or better yet, put a G17 at the start of your code, and it'll run fine.
N5 G17 (File Name = Testes2 on Saturday, December 11, 2010)
N10 (Default Mill Post)
N15 G91.1
N20 M5 M9
N25 M6 T2(TOOL Change 1/2" Cutter)
N30 G43 H2
N35 G0 Z1.0000
N40 M3 S10000
N45 X6.2500 Y3.0001
N50 Z0.1000
N55 G1 Z-0.1250 F5.00
N60 G2 X9.7500 Y3.0000 I1.7500 J-0.0001 F50.00
N65 X6.2500 Y3.0001 I-1.7500 J0.0000
N70 G0 Z0.1000
N75 G1 Z-0.2500 F5.00
N80 G2 X9.7500 Y3.0000 I1.7500 J-0.0001 F50.00
N85 X6.2500 Y3.0001 I-1.7500 J0.0000
N90 G0 Z0.1000
N95 G1 Z-0.3750 F5.00
N100 G2 X9.7500 Y3.0000 I1.7500 J-0.0001 F50.00
N105 X6.2500 Y3.0001 I-1.7500 J0.0000
N110 G0 Z0.1000
N115 G1 Z-0.5000 F5.00
N120 G2 X9.7500 Y3.0000 I1.7500 J-0.0001 F50.00
N125 X6.2500 Y3.0001 I-1.7500 J0.0000
N130 G0 Z0.1000
N135 G1 Z-0.6250 F5.00
N140 G2 X9.7500 Y3.0000 I1.7500 J-0.0001 F50.00
N145 X6.2500 Y3.0001 I-1.7500 J0.0000
N150 G0 Z0.1000
N155 G1 Z-0.7500 F5.00
N160 G2 X9.7500 Y3.0000 I1.7500 J-0.0001 F50.00
N165 X6.2500 Y3.0001 I-1.7500 J0.0000
N170 G0 Z1.0000
N175 X3.7500 Y6.2500
N180 Z0.1000
N185 G1 Z-0.1250 F5.00
N190 Y8.7500 F50.00
N195 X2.5000
N200 X1.2500 Y8.7500
N205 Y6.2500
N210 X3.7500
N215 G0 Z0.1000
N220 G1 Z-0.2500 F5.00
N225 Y8.7500 F50.00
N230 X2.5000
N235 X1.2500 Y8.7500
N240 Y6.2500
N245 X3.7500
N250 G0 Z0.1000
N255 G1 Z-0.3750 F5.00
N260 Y8.7500 F50.00
N265 X2.5000
N270 X1.2500 Y8.7500
N275 Y6.2500
N280 X3.7500
N285 G0 Z0.1000
N290 G1 Z-0.5000 F5.00
N295 Y8.7500 F50.00
N300 X2.5000
N305 X1.2500 Y8.7500
N310 Y6.2500
N315 X3.7500
N320 G0 Z0.1000
N325 G1 Z-0.6250 F5.00
N330 Y8.7500 F50.00