Form 8332 is a form that is signed when there are divorced or never married parents who both claim some child-related credits on their tax returns. You say your son is an adult--so what does 8332 have to do with this?
You say he did not work. What income did he enter on a tax return? Did he receive disability benefits? If his benefits are from Social Security, they do not "count" against the $4200 income limit that would prevent you from claiming him as your dependent. But if he did not say on his own return that he can be claimed, then your e-file will be rejected, and you will have to print and mail your return instead, He will need to amend after his return is processed.
It seems like we need some missing details about this, though. Your situation has not been explained fully.
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