Excel: How to Find Invalid References?

Solved for me. I had an issue with Excel not letting me save the file and keep complaining about:

"A formula in this worksheet contains one or more invalid references."

Some steps I tried initially, which as part of debuggig you should do first:

• Unhide all the cells and make sure there are no #ERRORS from #REF items.
• Use the Error Checking option via Formulas -> Formula Auditing -> Error Checking (this is completely useless for me though)

Finally, what solved the issue for me is actually deleting one of the charts. 

I.e., if you can't seem to find any #REF items but you have charts, try deleting the charts and see if the problem goes away! My problem is resolved after deleting one of my charts. I checked the chart (right clicking the chart -> "Select data") to make sure there were no #REF items, but it is casuing the invalid references problem nonetheless. I end up having to delete the chart and make a new one.