All I can suggest is to check that you have the correct paths to your image file. The code I posted above - if I recreate your structure and image filename - works correctly.
If you could put your page online, we could have a look at it to try to trace the problem.
Is this a SiteAssist/CSS Sculptor page? I'm not sure I understand what empty quotes you are referring to. Perhaps you could zip your page (and associated css file) too?