I just bought a Lenovo w530 with the upgraded Intel 6300 AGN adapter, and I've had this problem since I first booted it up. This ismy 3rd day working with my laptop, and every time I want to do anything online, I have to turn the wifi off then on, then wait for a minute to connect, and I have about a 5-10 minute window before I get "no network access".
The wifi signal itself is always strong, stable and never breaks. I have had this problem on multiple (2) networks that other computers have no problem with. It's definitely my laptop.