If the first byte is always nack'ed, then there is definetely something wrong. The first byte should always be ACKed if the slave part is functioning and the address is correct. Do you have pullups on the two I2C lines?

Also the PIC Basic Pro manual recommends not using a constant for the address byte. So either skip the address or use a byte variable.

i.e. I2CWRITE PORTA.1, PORTC.1, $4E, , [$A0, $00, $00]