This is not the first time I have seen this kind of situation, and unfortunately, there is no good news for you. This is a no-win situation, whatever you do.
You are presently a fugitive from justice
and have been for 16 years. Worse yet, you were convicted and sentenced 16 years ago. You were almost certainly told at the time of your sentencing how much time you could potentially be looking at if you failed to complete probation. As it appears you didn't complete it, if you return to Florida (or get picked up for any violation of the law anywhere else), you'll be returned, where you can be resentenced to the jail alternative that the judge warned you about. If you don't return to Florida, you can kiss your social security goodbye. That was Florida's way of getting your attention.
Your only possibility is to retain a Florida lawyer and find out just what you still owe probation. Maybe they made a mistake and you did complete it. Or,if it turns out that you only have some court fees (and interest and penalties) to pay, a lawyer might be able to help fix that so that you can avoid jail and then be eligible for disability payments. But if you just stopped reporting that's a whole other problem, and not one he'll be able to make go away. So even if you can't afford a lawyer, you can't afford NOT to get one, either.
About the only thing I could suggest to you would be to call the public defender's office in the county where your case used to be and explain your dilemma. They can't take your case, because they must be appointed by a judge. But sometimes they bend their own rules when faced with a defendant who has an emergency, and they certainly will know both the court and the judge. They can likely at least find out what the basis for your violation was and whether it's something that will be easy to fix, or whether the risks of long term incarceration are going to be high. They may also have a list of area pro bono lawyers or agencies for you in Florida.
One more source of free or inexpensive legal work would be a local law school criminal
justice clinic. Law students do a lot of good work on behalf of indigent community members, for course credit and under strict supervision of their professor/attorney. The professor would handle any court work necessary. They too would likely be able to find out the specification of your old warrant and find out what you're facing. However, you'd have to deal with one in Florida, not in the state where you presently reside.
Again, I'm sure this is not what you were hoping to hear. It is, however, the bind you're in. That warrant won't ever go away until it's lifted by the judge upon your voluntary (or involuntary) return to your old court. The denial of SSI is the first of many things you could find yourself not eligible for down the road.