Did a google and found this:
Q: He was wondering if corn syrup goes bad?
A: We called ACH Food Company, which makes Karo Corn Syrup. It says the shelf life for an unopened bottle of corn syrup is 720 days, or about 2 years. It says there's not really a shelf life for an open bottle because it would depend on the conditions it was kept it. Karo says you might want to consider throwing it away if the color or texture has changed.