JavaScript doesn't run on acrobat reader 8 (Continuation)

This message is related to the one posted today.
 
I'm attaching the script again at the end, altough i've already found the line where acrobat reader fails:
 
this.removeField(fieldName);
 
So, now i'm wonder how to solve this method call.
 
Thanks Thom, i could find the exact line by doing some debugging!!.
 
/* In the following script i've changed the less than symbol for < literal in order to have it well displayed */
var feimp=new Date();
var lorva='VALIDO POR EL DIA DE '+util.printd("dd/mmm/yyyy HH:MM:ss",feimp)+'.';
for(var pag=0;pag < this.numPages;pag++){
var fieldName='txtBtm'+pag;
var mife=this.getField(fieldName);
if(mife!=null) this.removeField(fieldName);
var aRect = this.getPageBox( {nPage: pag} );
var bRect=Array(0,aRect[1],60,0);
mife=this.addField(fieldName,'text',pag,bRect);
mife.display=display.noView;
mife.alignment='center';
mife.textFont=font.TimesB;
mife.textSize=18;
mife.rotation=90+this.getPageRotation(pag);
mife.value=lorva;
}
this.dirty=false;