I have no idea what happened but I just upgraded my phpbb2 board to phpbb3 and installed a new theme and my smilies are not showing in the post new thread or reply or any posts. I have checked the files and all the smilie graphics are there but they are just not loading. this is what happened 1) installed a new mode to my phpbb2 board 2) took it off and installed a new theme 3) upgraded the board to phpbb3 board 4) everything is working and default theme is there but no similes 5) installed a new theme but still no similes. checked the styles css files and images files and all are fine so what can be wrong.
I bet you it is a permission thing. If you right click where the image should be and get the location url of the image, paste it into a browser. If it tells you that you are not authorized to view, then it is definitely a permission issue. If it does not, then the images are just in the wrong location.
Neptune pretty much solved it but its probably the fact that its not in the right directory. Your theme is looking for the smiles in its theme directory even though the smiles are still probably in the old theme directory.