The smilies error can still appear even when there are none in a post - 'something' goes wrong in the background, while preparing the post, and that seems to be a pretty meaningless error the forum software coughs up as a result. I don't think I've ever seen this error unless I'm including an image in the post, though.
If, in desperation, the "Disable Smilies in this post" checkbox is checked, it's still hit and miss whether it will now succeed - it can sometimes work after doing this, but more often it simply fails with another error instead.
The best way to "test the waters" is to click the "Preview" button, whether images are included or not.
Any problems likely to cause an "error in posting" failure when submitting will surface then, plus it's an ideal chance to spot those text formatting or spelling errors. Although... sometimes, despite successfully previewing a post, submitting it can still cause the "error in posting" message - but in those cases, retrying the submission normally succeeds.
When no images are included this error appears to be very rare, and I can't think of any case during my own postings when it has appeared that a single retry hasn't then succeeded.
But when images are included and a preview generates the smilies error, it is sometimes worth trying the preview a few more times and if it succeeds, submitting the image immediately will also usually succeed. But if the preview never succeeds... well, it's a case of not including the image or trying another one from a different source - and it is source-related in some way: I have never had this error when posting images sourced through Wikipedia, for example.
@CheredIsTyping - no, this one is caused entirely by problems with the forum software. It's something about they way in which it processes a post in preparation for display (preview or post) that causes the error.
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Giraffe: a ruminant with a view.