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

One of the reason could be that the data that you are importing to PBI is  not in excel table. Select the rows and columns from the sheet that you want to import >> Insert Table in excel and try importing it should be able to read the data then .

Please use the Issues Forum for reporting bugs or issues like this one. Link: http://aka.ms/issues.powerbi.com

This Community Forum is aimed at allowing users to interact/share solutions or questions for how to achieve something with Power BI, rather than reporting specific bugs (we have a whole separate forum for that :))

When reporting the issue, it would be good to clarify whether you're using PowerBI.com directly or are using Power BI Desktop to import your Excel Workbook. If you're using Power BI Desktop, any spreadsheet data is supported (does not need to be a table), so if you're running into this issue there, chances are that the Excel document has some invalid parts that make it unrecognizable.

Thanks,
M.

Actually I don't think it is a bug.  The user that supplied the excel spreadsheet had hidden the tabs that had the actual data.  So technically PowerBI was correct.  Might want to wait to hear back from the user before closing out and not getting all the information.