Peculiar non-apperance of smileys in forum

Hi.

I can add smileys to comments in the forum and they preview fine, and the HTML appears correct, eg
<span><img src="../../smileys/packs/example/sad.png" title="Sad" alt=":(" class="smiley-class" height="15" width="15"/></span>

However they do not display when I submit and view the posting itself, just the alt tag value ':('. I get Watchdog 'file not found' errors ' for
http://example.com/smileys/packs/example/sad.png

I am using the Advanced Forum module and WYMeditor. The smiley filter is enabled for all input types. Any suggestions welcome!

Thanks /