It is not against the law, but keep in mind that websites are paid for and maintained by individuals or corporations, and as such are technically "private property". There are many banned members who do not have disabilities-the owner is paying for the site and he can determine whom he allows to post. I doubt that radio Reference has the requisite 15 employees to require ADA compliance on the website. That said, vBulletin software is completely ADA Compliant-so there are no violations.
Now, on to your post. I understand you have difficulties, so I'm going to ask a few questions:
1. What was the question you posted?
2. Where did you post the question? What forum/topic? Was it in the appropriate place?
3. Did you post the same question in more than one place? This is a violation of the rules that you agreed to when you joined.
4. I understand your disability causes some problems when constructing sentences. Have you made the board management aware of this disability? Have you used a text to speech software or other aid to ensure that what you are posting is understandable?
If a post looks like gibberish, you cannot expect people to understand what you are saying. If it looks like gibberish, people are going to report the post, and moderators are going to remove the post if no one can make sense of it. While you have difficulties, you cannot expect people to know that you have them without making people aware. There are more than enough nice people here that would be willing to help you, but to come in and just expect people to know what you mean by posting something that is not processed as a valid sentence is a failure on your part. The ADA is meant to provide a level playing ground for everyone regardless of disability, it is not meant to give those with disabilities an advantage over those without. Your immediate threat of a lawyer seems to indicate that you don't understand that.