[kh99]

Is it always exactly the same message, that is "Duplicate entry '7' for key 'PRIMARY'"? If the number increases by 1 each time the error happens then I'd say that the problem is that the postlog table somehow has more entries than the post table does. Did you maybe try to "reset" your forum at some point by truncating the post table (or maybe your attempt to import a database did it)?

In any case, you could probably just truncate the postlog table, since if you're only on post #7 I'm guessing it's a test forum and you don't care about the log info.