I had a hard time posting the previous post… oddly, WordPress kept informing me that I didn’t have permission to execute post.php, like this:
That’s rather disconcerting. A check on the server indicated that permissions were fine, no problems there. (Aside: they were 644, if you’re interested; I thought that this was the problem, at first, and changed them to 755, but this is not the issue. If your permissions are already 755, you may as well leave them, but 777 is not necessary, and definitely won’t help; you just made the post.php file writeable by anyone, and that isn’t even what we’re trying to do here. End aside.)
So, I did what anyone would do next; I plugged the error message into Google.
What I found was pretty strange; others were having this problem, but the issue seemed to be the presence of a particular word or words in the post; as near as I could tell, there are words/phrases which you can include in your post which will cause this error.
One fellow used the phrase “curl up” and got this error. (I duplicated this; in fact, the only reason I’m able to include those words in the post is that I used instead of a space between the two words.) Someone else suggested that “wget” might also cause this problem, but I haven’t duplicated that.
In the case of my previous post, it seemed to be the phrase “Flash player” — I hyphenated it when I isolated it, and voila — this solved the issue. It turns out I could have just used , but, oh well.
Is anyone else aware of more information about these “things you can’t say in WordPress”? Is this a documented bug? Is there a fix?
Inquiring minds want to know.

I had something similar happen, where I couldn’t post like that. It’s been awhile and I removed parts of my post until I narrowed it down to a specific word or phrase. I copied the original post back in, changed the offending culprit and it was fine. I didn’t google the issue at all, I just assumed it was isolated to me and didn’t concern myself with the source, although I should have. I was probably just busy and ready to move on. I don’t recall at all what the word or phrase was, but it was identical to what you describe. Sorry I can’t offer any insight other than I feel your pain.
Thanks for the reply, Jim. Yeah, apparently it is a wider problem with WordPress… I posted it mostly to add to the few other posts I found about it. If it’s a bug, it should be fixed; if it’s by design (blocking executable commands for security purposes) then there should be a list of words so that it isn’t just a shock when you’re told you have an error… ;-)