oh - 0xF7 isnt a correct SRF08 address...
i guess,
that is because of 7bit I2C addresses:
0xF7 = B11110111
0xEE = B11101110
0xEE (8bit address) --right-shift--> B01110111 = 0x77
so i guess ur new 7bit I2C address is 0x77 (which is equal 0xF7 modulo 128)... 