Have you installed Spreadsheet::WriteExcel properly from CPAN or PPM? i.e did not copy Workbook.pm or other dependent modules from other locations.
You may try this to update the module and check if the problem is getting resolved.

CPAN:
perl -MCPAN -e "install 'Spreadsheet::WriteExcel'"

Activeperl
ppm install Spreadsheet-WriteExcel
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