I think you are missing the control before the address of the I2C commands.

Also DEFINE I2C_SLOW 1 is NOT needed.

try this

Cont = %01000000

I2CWRITE SDA,SCL,Cont,[%11111111]
PAUSE 500
I2CWRITE SDA,SCL,Cont,[%00000000]
pause 500


Ioannis