This seems to be a reoccurring topic. I also am only returning an answer of 0. My equation is Region Percent * Geo Goal Set.Projected Goal[LOOKUP: Parent]. I have also ensured my Forecast version is current as well.
If Region Percent * Geo Goal Set.Projected Goal[LOOKUP: Parent] gives you 0, then at least 1 of the components is 0 or blank:
1. Region Percent
2. Geo Goal Set.Projected Goal
You can use the 'Drilldown' feature of Anaplan to find out which is 0 or blank, and proceed from there.