I get that error when I forget to disable my firewall software. I suppose that it's due to the fact that while the firewall is active, the BBS will not "see" a proper host IP address that the post originates from. Once I disable the firewall, the BBS allows me to make my post. After I'm happy with the post, I simply reactivate the firewall and all is well.
(ha ha, it just happened while I was trying to make this post, I just forgot what I was writing didn't I?)
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