The most likely thing I can think of causing that would be if the Estimated Low price was set to use 'Forecast Low Price'. Using that selection tells Toolkit to calculate a low price based on [Selected Low P/E] multiplied by [Estimated Low Earnings Per Share]
If one of those numbers is negative, then the entry for Estimated Low price would end up being negative as well.

I'm not sure about a change being necessary, given the number of options available for selecting a low price. If P/E times Low EPS is negative, there's always Average Low for the last five years, Severe market low, 80% of current price, etc.

Taking a step back though, a big part of the SSG is reading the past history, and making judgements about the future. If the low price is negative, and it happened because either Low P/E, or Low EPS was negative, then (to my mind), one of those numbers being negative is a judgement point.
Speaking personally, I either wouldn't have gone any further with that stock, or I would have been double-checking my figures, to sort out how I accidentally typed a negative for one of those entries.

On the other hand, if you're OK with earnings being negative (if you're bullish on Tesla Motors, for example), that's fine, but you would then want to make a judgement that P/E times EPS isn't a good way to calculate a future low price for a stock.

When calculating the Buy / Maybe / Sell ranges, 0.00 is treated as a null, or blank space, instead of a number of it's own. The calculation can't be started from there, so nothing gets filled in for the price ranges.

Edited by user Thursday, May 26, 2016 2:55:33 PM(UTC)  | Reason: Not specified