各位兄台帮我看看 无法识别的字符串 谢谢

Params
Numeric Length(26);
Numeric StdDevUp(2.0);
Numeric StdDevDn(-2.0);
Numeric Lots(1);

Vars
Numeric UpperBand;
Numeric LowerBand;
Series<Numeric> MidLine;
Numeric StdValue;

MidLine=Average(Close[1],Length); //编译不过，显示无法识别的字MidLine
StdValue = StandardDev(Close[1],Length);
UpperBand= MidLine+StdDevUp*StdValue;
LowerBand= MidLine-StdDevUp*StdValue;
PlotNumeric("UpperBand",UpperBand);
PlotNumeric("LowerBand",LowerBand);
PlotNumeric(" MidLine", MidLine);
If(MarketPosition!=1 &&CrossOver(Close[1],UpperBand))
{
Buy(Lots,Open);
}

If(MarketPosition!=-1 &&CrossUnder(Close[1],LowerBand))
{
SellShort(Lots,Open);
}

If(MarketPosition==1 && Close[1]< MidLine[1])
{
Sell(Lots,Open);
}

If(MarketPosition==-1 && Close[1]> MidLine[1])
{
BuyToCover(Lots,Open);
}

 

编译不过，显示无法识别的字符串MidLine