Check zone name (sbl-xbl.spamhaus.org) for typos.
Mr Linford of Spamhaus got so tired of people querying non-existent subzones of spamhaus.org that he configured his name servers to answer with 127.0.0.2 (in other words a DNSBL hit) every time anyone queried any non-existent subzone of spamhaus.org. For example:
$ nslookup 2.0.0.127.spl.spamhaus.org
Server: dns0.ns.uk.quza.net
Address: 195.166.13.4
Non-authoritative answer:
Name: sbl.address.is.wrong.spamhaus.org
Address: 127.0.0.2
Aliases: 2.0.0.127.spl.spamhaus.org
HTH
Chris Linfoot
http://chris-linfoot.net