PSP: How can I make a homebrew application work for my PSP?

You're probably playing games that require 1.50 kernel(psp slim doesn't have it) and switching the kernel to 1.50 in the recovery menu won't work with the slim because it doesn't have it. If you use the time machine on a href="http://dark-alex.org/" rel="nofollow"http://dark-alex.org//a you'd probably be able to use it(you'll need a pandora battery to use it)