You need a summary field in order to summarize a found set. The Sum() function (and other aggregate functions) summarizes mainly related records and repeating fields.
Once you have defined a summary field as Total of count, you can use it in your calculation instead of Sum(count).
Got it! You put me on the right track. One of my problems was that I had GrandTotalText designated as a Global field and it should not have been. Also, when I made it 'unstored...' it worked!
Thank you very much for the 'nudge' to get me in the right direction.