Thanks for the input....
I tried setting enable as an OUTPUT
pinMode(enable, OUTPUT);
no change. I didn't think PWM pins needed to be set.
On the other suggestion....
i = 255. I want to be able to vary this value to set an optimum speed for the motor. The problem is that only i = 255 works! Any other value doesn't. This is the value that is send to the 'enable' Pin to set the pulse width.... I don't understand what you "in init ()" does?