I found the way to fix the problem:
=SUM(IF(ISNUMBER(J2:J2500),J2:J2500))
...confirmed with CONTROL+SHIFT+ENTER, not just ENTER
___________________________________
I know how to make the errors go away with something like:
IF(ISERROR(G15/G14),#N/A,(G15/G14))
--but in this particular instance--- the errors are a good thing (an indicator) that we actually (want) to see --- because it points to a mainframe report that has either "no data" in places where it SHOULD BE......or points to a TYPO in the main frame field that needs corrected.....
Regardless, the user still wanted the ability to quickly calculate the total list to get an approximate sum ( Value of merchandise ).....aside from the small batch of items that need re-worked.....then, they'll go back later in the day and fix any items that are generating bad results.... Thanks for taking a second to look at it --- Hopefully, this will help others with similar scenarios...