I think you've got to adjust your parameters.... This was on another site helping somebody with a similar problem...
"try M21 advance M22 retract but you will have to adjust a setting in your parameters. I forget which one it's in the 90's or 100's. hope this helps"
If that don't do it... http://www.fanuc-spares.co.uk/fanuc_parameters.htm
this website might be worth looking at for kicks..