If I meet all 4 qualifications for the retirement credit, why am I not able to calculate it? Why do I receive a message saying I don't qualify?

[dmertz]

It's often because one's income tax liability is already zero without the credit.  This is a nonrefundable credit, so it cannot be used to reduce your income tax liability below zero.  It also cannot be used to reduce other taxes such as self-employment tax or early-distribution penalties on distributions from retirement accounts.