Step 1: Download the REBUG Toolbox from the link above and take a USB thumb drive and copy the REBUG Toolbox to the Root of the USB.
Step 2: Take the USB and plug it into your PS3. REMEMBER You must be running REBUG Custom Firmware in order to use the tool box!! Go to your Packages manager and select Install Packages and select Standard and install the REBUG Toolbox.
Step 3: Run the REBUG Toolbox from the XMB and scroll to Selector. Make sure to enable REBUG Mode, Cobra mode, Change PS2 EMU to Cobra, and Enable WebMAN. Exit the toolbox and your system will reboot.
Step 4: After your PS3 Reboots, If you havent already place an ISO for a PS2 game in your /HDD0/PS2ISO folder Using MultiMAN and then mount that ISO. Run it from the XMB and your game should work just fine.
NOTE: Be sure to set your Virtual PS2 Memory Card to slot One before booting the Game.