'unknown error'

The network these logs are from, used to run bopms approx. 6 months ago and stopped for a while and has now restarted to use them. They are newly compiled bots/binaries, with the corresponding config lines copied across from the old config file. The old bopms ran smoothly without problem, however, the news ones more often than not, produce lookup errors:
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[21:47] <Port3> DNSBL -> [email protected] appears in BL zone opm.blitzed.org (Socks, HTTP, HTTP POST)
[21:48] <Port5> DNSBL -> [email protected] appears in BL zone opm.blitzed.org (HTTP POST)
[21:48] <Port6> DNSBL -> [email protected] appears in BL zone opm.blitzed.org (HTTP POST)
[21:48] <Port4> DNSBL -> Lookup error on 72.177.212.81.opm.blitzed.org: Unknown error
[21:49] <Port3> DNSBL -> Lookup error on 58.216.116.212.opm.blitzed.org: Unknown error
[21:51] <Port5> DNSBL -> [email protected] appears in BL zone opm.blitzed.org (HTTP POST)
[21:53] <Port5> DNSBL -> Lookup error on 112.27.204.24.opm.blitzed.org: Unknown error
[21:54] <Port6> DNSBL -> Lookup error on 198.156.69.200.opm.blitzed.org: Unknown error
[22:01] <Port6> DNSBL -> Lookup error on 236.96.86.81.opm.blitzed.org: Unknown error
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The only error it produces is the 'unknown error' and as it can perform working lookups, i don't understand why only some of the time it produces the unknown error.
I asked someone else about the error lines before coming here and they said the error was in the DNSBL, and therefore was not a setup/comp problem but, however, was a problem with opm.blitzed.org itself. Is there a simple config error which can be easily fixed, or is it infact your problem?
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