Is there a differance between a conviction and deferred adjudication case when it comes to owning a Firearm?

My question is I had a felony Deferred Adjudication: Probation case for Marijuana and I was told by my lawyer I would not lose my right to vote or own firearms. 2 years ago I applied for a FOID card in IL(we need that to own a firearm)and was denied my card because of this. I now live in GA and all you need here is the 3 day waiiting period to own a firearm I dont want to suffer the the embaressment of trying and I would really like some info on how to proceed with the Motion for Non-disclosure if that would help. The question I really want to know is am I able to legally own a Firearm? This case was in 1996 when I was young and dumb I checked with the courthouse and they said it was not a conviction but a deferred adjudication so I guess my other question is why was I denied a FOID card?