vtec malfunction question

i have a 99 civic SI with basically all stage 2 skunk 2 internals in the head, full exhaust (header back) aem fuel system, adn other things, i am throughing the code P1259, Vtec system Malfunction , my car is running not so good right now, VTEC is still kicking in but it is being tempermental, does anyone have any ideas as to what i should check other than electrical and oil levels....and suggestions are appreciated

I had that problem and it was that I didnt have enough oil and that turns off the vtec once in a while anyways if you have checked that try checking your vtec solenoid that can be the problem also, if not I dont know good luck!!!