That's not a known DominoWiki error… I notice your Domino server is using "!" rather than "?" in the URLs it generates, but that shouldn't cause a problem. My one thought was that this had something to do with the spam protection I've built into 1.2, but I don't use that text in any of the error messages, and the error message would be styled in any case.
It looks like the Domino server is configured to reject the content being sent to it, but I can't tell you more than that at the moment – do your logs shed any light?