Guy please, I have question. It is confirmed that you must be on 3.55 FW/CFW to install this 4.21 CFW. Or this is not 100% confirmed? I read at source of Red Power Team. And one Chinese told me on forum this:
"yes, if you have a 4.xx fw ps3, you need to downgrade it first and if your ps3 console cannot be downgrade, then you can't install the RED POWER too. RED POWER FW don't have downgrade function RED POWER FW only works with 3.55 FW, so this don't have too much sense and the most important is, It's not free"
So that CFW is not for 3.55+ FW users. I repeat who have installed example 4.00 FW. He can't install this CFW.