Mitsubishi M-H60EN horizontal mill high feed milling help

We have a Mitsubishi M-H60EN multi pallet horizontal mill. When I high feed mill, not even going 200ipm, the bore or slot cuts undersize by .100". I tried using G5P1 which is supposed to be High Feed mode, but I get an error P63 No G05 SPEC, which I assume means I don't have the option. I also tried a G61.1 which is High Precision control mode, and it looks like it is supposed to address this issue, but I get P123 No Pre-Intp I'm guessing pre inp means pre interpolation, but I don't know what that means. Has anyone run across this?