why the backtest did not work?

[bmx888@xxxx]

I am not sure I understand this. The following system has only one 
trade on 4 years of data and with every stock I tried. Something is 
wrong and I can not figure out why. Any idea?

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BuyStop= ref(HHV(C, 20), -1);
SellStop= ref(LLV(C, 20), -1);
BuyPrice = max( BuyStop, Low ); 
SellPrice = min( SellStop, High );
Buy = Cross( High, BuyStop ); 
Sell = Cross( SellPrice, sellstop);