hi. first all. i would like to tell you... if you downgrade your bluray may can not read bluray dvd films. when you use downgrade your upgrade you must use new self file. for use first step downgrade. beside. you should back up your dev_flash3 folder you are already in 3.41 for downgrade you make your jailbreak to downgradable so you must setup normal jailbreak format again.
if you dont do. ps3 can not recognize of course. and after i also had this problem before. just download new 3.55 cw and also for knaew 355 , after download normal flash disk open a folder called PS3 and inside again open a folder called UPDATE (PS3/UPDATE/PS3UPDAT.PUP format.) and then put your offical 3.55cw inside and just go to update section from flash disk.
it should upload without problem. for update kneaw the same way. but this time it will give error. you should set up by service mode. not for jailbreak help. just hold your power puttong some second to hear two bib sound. ps3 will close again open and hold your hand to pwer putton after hear two bib sound take your hand and you will see service mode.
after use upgrade and start +select togeter and it will update. while you may need to use your ps3 controller by usb contact. i wish it will help you more clearly.