Hi Peter,

A couple of things I've spotted:

1) If you are using different timeframes, I think you need different series for the price hi,lo,cl in each or simply call the relevant price().

2) HH & LL are built in functions that take a period parameter. you are declaring them as a series of vars and assigning them the value of price high or low for the current bar.

3) midpoint is H+L/2.

Code:
function run()
{
// 4 hour (240 minute) bars used in this strategy 
StartDate = 2014;
BarPeriod = 240;

// = MTF Pivot Point
// timeframe 6 * barperiod 240 = 1 day bar
TimeFrame = 6;

// define BIAS calculation
vars BIAS = series(((HH(3)+LL(3)+priceClose(0))/3));

// back to 4 hour time frames
TimeFrame = 1;	

// describe MB calculation
// = midpoint of bar()
vars MB = series((priceHigh(0)+priceLow(0))/2);

// if C() > MB[] // then close above midpoint
// if C() < MB[] // then close below midpoint

plot("MB",MB[0],0,GREEN);
plot("Pivot",BIAS[0],0,YELLOW);
}