How to handle this error on an import Results page:
Error, ExcelImporter, constructor: Unspecified error (Try changing the Excel worksheet name to 'Sheet1').
This error can occur when the import file contains a multitude of empty rows after the last data row.
Excel will sometimes clear rows instead of deleting them. You must select rows from the bottom up. Click on the last empty row, move up to the first empty row, and delete. If you select the rows in the opposite direction, Excel will clear them instead of deleting them. If rows were actually deleted, the saved file size will descrease.
Alternatively, you can copy the data rows without the empty rows to a new Excel file. Again, the resulting file should be smaller.