This part:
INNER JOIN sponsorcategories ON sponsors.SponsorID = sponsorcategories.CategoryID
Should be either:
INNER JOIN sponsorcategories ON sponsors.SponsorCategoryID = sponsorcategories.CategoryID
or:
INNER JOIN sponsorcategories ON sponsors.SponsorID = sponsorcategories.CategorySponsorID
The two keys aren't what match to create the join. It would be a key in one table joined to the associated field in the other.