Now that you are on OFW 6.60, you have two modern choices: or 6.60 ME-2.3 . 6.60 PRO-C2: Highly compatible with almost everything. Copy the PROUpdate and CIPL_Flasher folders to PSP/GAME/ .
Upgrading a PlayStation Portable (PSP) from the legacy custom firmware to the modern
Now that you are on OFW 6.60, you can install modern custom firmware.
Installation checklist (concise)
Go to Configuration and ensure "Use version.txt" is set to Disabled . Exit: Select Back and then Exit . 3. Step 2: Updating to Official Firmware 6.60
: Update to an intermediate firmware like 3.52 M33-4 or 3.71 M33 if a direct update fails.