I would like to delete my question here since the problem was due to human error but I am being warned that I could be blocked:
How serious is the warning? Or can I just proceed without worry?
It's a warning meant to make you consider the deletion. So, you should pause to think: does this Q&A pair add any value to the Internet? If your answer is confident no, go ahead and delete.
It is true that deleting many own questions is a factor in automatic question blocks (now rolling time-limits). However, a user with 1000 rep and many well-received posts is unlikely to hit those. You can ignore the second paragraph unless you are on a self-deletion rampage.
Also, note that the system will still block the deletion in the following cases:
In the specific case, it seems the answer might be removed anyway, since it's downvoted and has drawn a vote to delete. When/if it's gone, you will be able to delete the question.