You need to do the "GEN Bypass"
1. Press select to access VSH menu
2. Set USB DEVICE to "flash 0"
3. Connect to PC and search for the folder "etc"
4. Locate version.txt , open it , you'll see a number X.XX right beside the word release at the top
5. Change the number to 5.50 , save changes , exit USB mode
6. Set USB DEVICE to "Memory Stick"
Now update as you normally would either through network update or manually