Same issue here using Excel 2011ver 14.3.6 on 2.7ghz i7 Powerbook running OS X 10.8.4
"Excel could not open draft_buddy_football_2013_1.0.xlsm because some content is unreadable. Do you want to open and repair this workbook?"
Tried re-downloading 5 times over the last couple of weeks, downloaded the xls version, copied to a usb drive and tried opening from there, downloaded with Safari and Firefox, still receive error.