It might be because your picture is too big. First off - 15 colour golden rule (16 actually, but one's transparent). Try to minimize the picture until it can fit unless you want to find the pointer to the picture, and I'll tell you one thing, it's not easy to find that pointer.
Also, if you're using UNLZ, use Black and White mode. That helps.
Title screens are annoying, to be honest. I actually haven't been hacking for a while so you might want to ask someone who regularly attends that area however.