Iwant to update Samsung Galaxy S gt I9003

Hi! I'm using Galaxy SL 4GB(GT-I9003) in India. 1) Firmware version : 2.3.6 2) Baseband version : I9003DDKP4 3) Kernel version : #1 4) Build number : GINGERBREAD.DDKP3 I try to update this phone to ICS but getting error of E:signature verification failed... it appears in red letters and then it aborts the installation. So Pls help me to fix this error Waiting for your reply. Thanks in advance!

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