[amibroker] MACD () not liking parameters

[gmorlosky]

The m = MACD() doesn't like when I use Mymfast Mymslow Mymsignal in 
place of mfast mslow msignal. Why is that ? 

pds = Param("pds", 2, 1, 10, 1 );
VolROC = 1 + abs(ROC( EMA( C, pds ), pds ) / 100);

mfast = Param("MACD Fast", 8,8,15,1);
mslow = Param("MACD Slow", 17,17,30,1);
msignal = Param("MACD Signal", 9,6,15,1);

Mymfast = mfast *VolROC;
Mymslow = mslow *VolROC;
Mymsignal = msignal *VolROC;

m = MACD(mfast, mslow); 
s = Signal(mfast, mslow, msignal);