I just recently had this problem. It ended up being related to a Stock ticker that was delisted: USCR.
Once I finally recalled that USCR had been bought out, I went to the cells that contained the USCR stock market reference, and I noticed that Excel had flagged the cell with a little blue triangle in the corner of the cell. When I hovered my mouse over the cell, it indicated that it was indeed the culprit causing the error message. So I reentered USCR manually, and used Ctrl-Z to undo the auto conversion to a stock ticker, and replace the old stock quote with a manual one. And now I no longer get the errors.
I would love it if there was a way to have Excel jump to flagged cells.