Except that I fell for your mistake, and that's not how I2CWRITE works:

I2CWRITE DataPin,ClockPin,Control,{Address,}[valvue{,Value...}]{,Label}

ie.
Code:
I2CWRITE PORTC.4,PORTC.3,$ao,0,[STR a\8]
I think you set the command to look for another I2C device on the bus rather than incremented the address index for the same device.