Including many images almost always seems to cause problems, and sometimes even one image does too. I've experienced it a couple of times with one image - either a simple "Error in posting" message or more commonly, "Can't obtain smilies data".
In your third post you said that editing the post got it to eventually work - is that now not the case?
If this error is going to occur it usually occurs on preview too, so a preview can be used to "test" the situation before posting.
When I've had this error on posting I use the browser's "back" button to return to my post edit screen and then attempt a preview - firstly to see if it works and secondly to see it my post was actually made, despite the error. You can always see the most recent post to a thread below the "preview" area and sometimes, there's my successful post.
Amongst these are actually the resolutions for the problems I've had, and I've only had repeated failures where there was something weird with the image file itself. That's unlikely in your case as you're posting images from the same webcam source.
The upshot is that it appears to be a problem with the forum software and there's nothing we can actually do about it, since it requires the code to be pulled apart and re-written, and that's well outside our remit.
I'm afraid that the only thing available at the moment is "try again".
Sorry.
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Giraffe: a ruminant with a view.