DavidR - never ever press PREVIEW button when you are posting something with attachment included. Your attachment will be lost as soon as you press PREVIEW button. When you finish typing your post, and attach attachment (in this case it's a picture), immediatelly press POST button. Try it and you'll see... 
Cheers everybody !
Never do use Preview when posting attachments, I learnt this within the first few days, I think I mentioned this some time ago about, the file not being uploaded until Post is executed, but Preview doesn't upload the file but records the filename so it can't used again.
This time it disappeared into the bit bucket, I can only put it down to a possible time-out as the forums were slow at the time, I don't know for sure just that it disappeared.
I rarely use the Preview now anyway, as the time to preview on a dial-up connection is a waste. Even worse when the forums are slow.