Image link works in dev but not in staging

Content

Hi,

I have an image saved in themes/standard/images folder and I refer to it in a widget base.css file as a background image url. The image shows in dev but when I stage it I see in Firebug 'image not found'...

The css is as below.

I have other images saved there and they all load correctly on the same page.

Have I missed something?!

Version

Aug 15

Code Snippet

             .rn_AnswerFeedbackAndPolling .rn_AnswerFeedbackControl button div.rank_0 {
    background: #999999 url("images/tts-smileys-transparent.png") repeat scroll 0 0;
}