There are different rules for SS retirement eligibility and for SSDI eligibility. http://www.ssa.gov/retire2/credits3.htm

I had actually revised my last post on the prior page. Does that help?

Sorry if I'm confusing you.

Here's a link to SS calculators. http://www.ssa.gov/planners/benefitcalculators.htm

What I wanted you to understand from the link was that you apparently have years with no credits and reduced credits. That's likely the ineligibility problem.