No problem happens for me too. Life is playing his game and sometimes i have a lot to cach up
You need a hardware flasher but for what i have read E3 is worst in case of the non-check limitation. So get a ProgSkeet or do your owen one or use the teensy2++. If you not skilled for that just get ProgSkeet and buy the x360 clips or wait for there owen cheaper clip version.
Dump your NAND and save the backup. On HDD backup act.dat and everything in HDD/Home. Normally it shouldn't efect this folder but just to be sure. When you have everything backedup install OFW you want to get the new BD-FW with decryption keys on the drive.
After successfull update just flash back your previous made NAND dump to gain back your CFW and his last stat.
ps. Your much as save in case of your NAND dump which is a 1:1 copy of your PS3's brain and your base version is 2.70 which means it is one of the first version's and can be down/up graded as much you want without any troubles.
pps. If it works and you gain the new decryption keys you can make a TUT or tell me and i will do. Good luck and let us know if your lucky on the end