Why doesn't the BidScreen XL ribbon tab appear in Excel?

The most common cause is a 32-bit / 64-bit mismatch between Excel and BidScreen XL. The BidScreen XL installer must match Excel’s bit version. Verify Excel: File → Account → About Excel; the bit count is at the end of the first line. Reinstall the matching BidScreen XL build, then add the .xlamfile via File → Options → Add Ins → Go → Browse.