there have been a few exploits since GTA. The latest is for 5.03 and uses a tiff image. There is also one for below 3.5 using Lumines and one for 2.8 and below using a tiff image. i'd recommend doing as xist said and upgrading to 5.03, using ChickHEN to run Hellcat's Recovery Flasher and installing 5.00m33-6 (NOT 1.5, this is a CFW, much better than 1.5, this has more features, and can use modern homebrew, which 1.5 can't. CFW can also use plugins, has ISO loading built in and uses POPS for near-perfect PSX emulation). Here's a summary of all exploits that can be used to downgrade:
TIFF Exploit [eLoader] – 2.00: Used a bug in libtiff to run unsigned code, this exploit was patched in 2.01
GTA:LCS Exploit (GTA:LCS) [eLoader] – 2.00 to 2.60: Used a modified savegame to run unsigned code, can be used to downgrade in 2.50, 2.60, save slots 1-7 were patched to prevent this exploit in 2.70
TIFF Exploit [eLoader/HEN] – 2.01 to 2.80: Used a bug in libtiff to run unsigned code, can be used to downgrade in 2.01, 2.71, 2.80, this exploit was patched in 2.81
“Goofy” Exploit (GTA:LCS) [HEN] – 2.00 to 3.03: Used a modified savegame to run unsigned code, this exploit is different than the one for firmwares 2.00 to 2.60 as it uses save slot 8 instead of slots1-7, Sony patched slots 1-7 but not slot 8, can be used to downgrade in 3.03, this exploit was completely patched in 3.10
Illuminati Exploit (Lumines) [HEN] – 1.50 to 3.50: Used a modified savegame to run unsigned code, can be used to downgrade in 3.11,3.50, this exploit was patched in 3.51
Easter Eggsploit [HEN] – 5.00 to 5.05: Also called the “Laughing Man Exploit”, uses a bug in the way Sony implemented libtiff to run unsigned code, can be used to install CFW on 5.03*, this exploit was patched in 5.50
Looks like you'll have to upgrade to 5.03 unless you have an old copy of lumines (new copies are patched i think). So upgrade to 5.03 and use ChickHEN.
