Make a new folder called "UPDATE", in all caps and place the 3.03 update in the folder and and rename it to "EBOOT.PBP " Then go to XMB > Game Memory stick and run the update then downgrade as normal to 1.5. Then Update to 3.03 OE-C.
3.03 Update:
File Details-Firmwares -

3.03 Downgrader:
3.03 Downgrade Tutorial - PSPMod.com - Sony PSP Mod & Hacks Forums

3.03 OE-C Easy Installer:
/forums/showthread.php?p=112210#post112210

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