Has anyone seen this error before?

I have a large workbook with lots of VBA code in it. I know how to set breakpoints and step through code.
I have a Validation Dropdown that displays a List that is created by a Dynamic Named Range.

When I click on the validation dropdown arrow I get the following Error message and Excel ends up shutting down. I'd set a breakpoint if I knew where.

Hints, please... Here is the screen shot of just before Excel closes.

2016-07-28_9-06-29.jpg