well do you know that what are you saying related to downgrade a 4.11 to 3.66 to 3.55 via software is impossible ?? how it can be 3.66 have a bug ?? that make you install it via recovery on a higher firmware and then make you downgrade always via recovery on a lower firmware ??
like other here are saying to you just get a progskeet or a E3 flasher it depends if your PS3 is NAND or NOR there is a list available somewhere not difficoult to find so that you can understand it before you open your PS3, then proceed to downgrade ..beware OLD NAND PHAT PS3 are a hell for downgrade.
all friend today i give you little prove of downgrade ps3 (all friend if you install 3.55 firmware on 4.11 ps3 say that (3.66 or later version install 8002F2C in ps3) its all ready define it mean you need only simple firmware 3.66 (not jailbreak 3.66) in this case you must downgrade successful (i downgrade 14 people ps3 with this method) (that all)
Dantesparda3 that work i get same error (3.66 or later version install 8002F2C in ps3) yeah i downgrade successful that work GOD bless you for every day (every one that work dantesparda3 idea is work 100%)