I run this code from the POD and get the expected output, given the Excel 97 - 2003 formatted file I used:

Row, Col    = (0, 0)
Value       = 1
Unformatted = 1

Row, Col    = (0, 1)
Value       = a
Unformatted = a

Row, Col    = (1, 0)
Value       = 2
Unformatted = 2

Row, Col    = (1, 1)
Value       = b
Unformatted = b

Row, Col    = (2, 0)
Value       = 3
Unformatted = 3

Row, Col    = (2, 1)
Value       = c
Unformatted = c

Row, Col    = (3, 0)
Value       = 4
Unformatted = 4

Row, Col    = (3, 1)
Value       = d
Unformatted = d

Row, Col    = (4, 0)
Value       = 5
Unformatted = 5

Row, Col    = (4, 1)
Value       = e
Unformatted = e
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Changing the format to Excel xlsx returns the same error you report, this suggests you are using an unsupported format (xlsx) with the file extension xls. Note the second line of the module description:

"The module cannot read files in the Excel 2007 Open XML XLSX format. See the Spreadsheet::XLSX module instead."