Summary field not working--suspect key and reference field issue

I have tables for Project Forecasts and Project Tasks (which include revenue). Each of these tables has a field, Project Number.  On each Project Forecast, I want to summarize the revenue for a given Project Number(so that the forecast and actual revenue can be compared).  Here is the relationship:

Project Forecasts  -----------------------------E Project Tasks
key field: Record ID                                  reference field: Related Forecast
Summary Field: Total Revenue

However, the summary field never pulls in anything.  I suspect this is because the Record ID and Related Forecast don't match.  I can get a report link field to pull in the correct records, because I can change both the key and reference field to Study Number, but this won't work because I need to be able to summarize the data by type of study, project manager, etc.

I also tried creating a relationship where the reference field was a lookup field of the Forecast-Record ID but it wouldn't let me create a summary field.  I saw in the forums that I could populate this Forecast-Record ID field through a form rule, but that won't work because the forecasts are intentionally filled out via grid edit.  

Help :)