No one reads anything
Lets get this out of the way to begin with; no one ever reads anything unless they are made to. It's a sad fact, but it is a fact none the less. So as helpful and crystal clear as this message box is people will still not read it.
For example this person says they didn't realise they weren't supposed to post follow up questions as answers right up to the point they were banned. And I believe them; it is just human nature. Forums also don't help with this because you do "answer" there with follow up questions, clarifications etc.
After a deleted answer give a message that you have to read on your next answer
The answer to this of course is to force people to read something. By presenting the message and then not enabling the "ok" button till a timer has elapsed there is no option but to read the message. This would reuse the functionality from some of the review queues.
This is designed to encourage anyone who doesn't read dialoges to click "This doesn't answer the question", the only way to actually answer is to wait 5 seconds (during which you may as well read the message) and then click "This answers the question".