The bid price is negative, so:

Code:
void tick()
{
	T1* Ask = dataAppendRow(1,2);
	Ask->time = wdate();
	Ask->fVal = priceClose();
	T1* Bid = dataAppendRow(1,2);
	Bid->time = wdate();
	Bid->fVal = -(priceClose()-Spread);
}