Run-time error 1004 when closing workbook that has no macros

Details will be a little sparse as I'm trying to answer a coworker's question to me. They have been working with me to create a macro to automate condensing some data and applying it to a pre-formatted template sheet for use in a report.

While doing some clean-up actions I suggested (removing screen scrolls & such that got captured when they recorded some steps) they started having Excel throw a 1004 when closing files.

The issue apparently occurs both when the macro-enabled workbook I'm helping with is open, AND when they have no workbooks with macros open.

What's more frustrating is the Debug button is disabled in the error window. So there's nothing to really provided any idea where the error is originating.

Has anyone seen anything similar to provide ideas on how to even troubleshoot this?