Have you considered going through your server and/or firewall logs to find out the root cause of the issue? Your host should be able to help you there, even without any IP's. Just run a crawl, and tell them approximately what time you ran it - that should be enough for them to start analyzing the issue.
The first question to find an answer to is what is blocking the crawler, followed by how is it blocking the crawler and finally, why is it blocking the crawler.
Once you find an answer to those questions, it will be vastly easier to help you find a solution.