Error Code -24, Tried Almost Everything!

[inthesummerrain]

Hello, all. Today I ran into a problem with my Galaxy S2 (rooted, my cousin did it, he handles all that stuff for me) and it froze at teh AT&T logo everytime I tried turning it on again. It eventually turned on by itself, but I believe reset itself.. I still had apps, texts, photos, music, etc except Contacts because they weren't on my SD Card. Anyways, I realized one of my apps weren't on there- Pixlr Express. I tried redownloading it and got the -24 error message. I plugged the phone into my computer, and searched Pixlr and deleted two files... None of which started with .com... No idea how to solve this now! Still getting the error -24. Tried rebooting as well.

Android Newbie! Please explain like you would a 12 year old!