I'm sure I read this here already but I thought I'd post it up in the tips section.

Several (including me) have reported problems setting the CC on occasions. I was unable to identify the circumstance that caused it and I had just accepted that it was probably related to heat until now. There may be other causes but...

..the CC will not set at all until the brake pedal has been pressed, at least once since starting the car.

I guess the logic is to ensure the brake switch can disable the CC to prevent "runaway".

If your CC will not set, try tapping the brake then try again.

[henridr]

i think you give me the respons of one situation i have got with my new I30, i didn't understand this time why i couldn't activate the CC, the brake was probably the origin

thank"you Pip for this precision  .
Henri

[Lorian]

And of course if the brake light switch is fault it won't set (this would seem to be more common than you would expect, possibly indicating a quality issue for some production)