BOPM Problem

I'm getting a Server Failure every time people connect to my server.  
I've used the same stuff for months, maybe even years without any 
problem.  I haven't changed anything, I just randomly started getting 
all these server failures.  I've looked through FAQs and docs, and the 
only thing I can find is something about not using opm.blitzed.org, but 
as far as I know, I'm not using it anyway.  Here's an excerpt from my 
bopm.log.

[Apr 26 07:50:50 2009] DNSBL -> Lookup error on 
20.145.64.72.dnsbl.dronebl.org: Server failure
[Apr 26 07:58:15 2009] DNSBL -> Lookup error on 
84.117.115.208.dnsbl.dronebl.org: Server failure
[Apr 26 08:09:20 2009] DNSBL -> Lookup error on 
52.141.25.85.dnsbl.dronebl.org: Server failure
[Apr 26 08:20:50 2009] DNSBL -> Lookup error on 
20.145.64.72.dnsbl.dronebl.org: Server failure
[Apr 26 08:50:50 2009] DNSBL -> Lookup error on 
20.145.64.72.dnsbl.dronebl.org: Server failure
[Apr 26 08:51:30 2009] DNSBL -> Lookup error on 
248.14.87.203.dnsbl.dronebl.org: Server failure
[Apr 26 09:00:15 2009] DNSBL -> Lookup error on 
89.217.26.216.dnsbl.dronebl.org: Server failure
[Apr 26 09:09:20 2009] DNSBL -> Lookup error on 
52.141.25.85.dnsbl.dronebl.org: Server failure
[Apr 26 09:20:50 2009] DNSBL -> Lookup error on 
20.145.64.72.dnsbl.dronebl.org: Server failure
[Apr 26 09:42:40 2009] DNSBL -> Lookup error on 
168.56.192.74.dnsbl.dronebl.org: Server failure