jQuery Themeroller-can't create my own image

jQuery Themeroller-can't create my own image

Hi,
I'm very new to jquery and Themeroller, but I have a question.

I successfully used the tabs and the images that are generated through the custom Themeroller.  But I want to further customize the tabs into my own design, but when I do that,  using the same size and changing out the pngs, keeping the exact file name, it doesn't show up.  I then go back and substitute back the png from the Photoshop file I created (using save to web), and it works great.  Why is the file (css) not taking my design which is the same mode, size and file name?

I've attached two files, (ui-bg_glass_75_0438f0_1x400.png) is what jquery themeroller accepts and displays.  The one,  ui-bg_glass_0_0438f9_1x400.png  is my version but will not display (yes, I made sure that the file name matches the call out in the css.

Thanks for your help.
Janell