It looks like the 1.5 firmware exploit you're using doesn't work. But I've had no problem using "SeiPSPTool.exe" to convert it over to a usable format, but the 1.5 version you included in the archive just gives an error. It could be the folder name, I'm not too sure. But using that tool, it works fine.
BTW, what about allowing the end user to make up different sets of backgrounds and number/icon sets, using some kinda set of image files? And maybe even an option to randomly pick a different icon/background sets each time the game starts? And/Or use one of the PSP buttons to change sets? There's alot of unused buttons there.
I just keep asking for features! It couldn't hurt to ask, right? :D