GETTING THIS ALERT: Excel ran out of resources while attempting to calculate one or more formulas.

It's possible the usedrange extends well beyond where your data actually ends. If you were on a PC, I'd suggest Inquire but I see you're on a Mac. I'd try going through each sheet and pressing Fn ^ (right arrow) to see what Excel sees as the end of your data. If it jumps well beyond your data, then that's the cause of the memory error. You'd have to select the excess and delete the rows/columns.