Electronic stability control help

[Devious25]

I have recently put new tires on my 01 Audi and from then on my esc light will come on and i get loss of power. It mainly happens when picking up speed. But it doesnt happen all the time. What could be the problem

 

[Nitro]

This might sound stupid but are you sure they fitted the correct size (rolling circumference) & is it a quattro? New tires also need time to bed in before they grip properly