choppiness index indicator

["john Davis" <buglywugly@xxxxxxxxxxx>]

would somepne take a look at this indicator, and tell me why it says:
"tried to pass a 0 or a negative value to the log function" and what
to do about it? I would appreciate any help
                                                                            
                   John


{Indicator: Choppiness Index}

Input: Ndays(9), avgLen(6);
IF Currentbar>=1 then begin
	Plot1(ChoppyIndex2(NDays),"Plot1");
	Plot2(50,"Plot2");
	Plot3(xaverage(ChoppyIndex2(nDays), avgLen),"Plot3");
end;