The error seems to arise in the bolded section above.
If I break each section down, eg, I insert =ADDRESS((ROW()-$M$7),2,4) into its own cell I get the correct result for this portion of the overall formula. It gives the result of a cell reference (B10 in this example)
If I insert ADDRESS((ROW()),2,4)) into another cell it gives me the right result (B35 in this example).
When I add these two components together in a SUM formula it falls apart SUM(ADDRESS((ROW()-$M$7),2,4):ADDRESS((ROW()),2,4))
In the bold section I am trying to arrive at the result of SUM(B10:B35).