The input couldn't be recognized as a valid Excel document

Hello everyone.  Long time lurker, first time poster.  

I'm working with another department on getting some of their data into PowerBI from excel spreadsheets.  When I load the file to PowerBI I get a simple yet very frustrating error message of...

The input couldn't be recognized as a valid Excel document

Now this is a very complex spreadsheet with multiple tabs and lots of data.  Any commonly known issues that would prompt this error?