if you have changed your hard drive put the original one back in an try updating... the 3.56 update killed a lot of ps3's that updated without the original hard drive... i just got mine back from being serviced by $ony... cost me $100... i had the same issue but didn't have original hard drive to fix it.
I was on 3.41. Bought Gran Turismo 5 and it asked me to update to 3.56 (through the game disk)- did that, it got to 100% and after words there was a little pause and then the error message "update data corrupted (8002F157)"
As part of the solution- I formatted the HD - first through PS3 and after I saw that it didn't help- I formatted trough the PC. Now I understand that I shouldn't do that...
Does anyone here know of someone that sorted this out?