WiFi connected-internet unavailble

I have a peculiar WiFi issue in my office where I can connect to the router, however, I immediately receive a message: "internet unavailable". I am using latest stock T-Mobile ROM. 5.01, Build 20E. Other phones have no problem like my Nexus 5 or other people's iphones. Also, I am running a dualboot partition with a nightly on the same phone and it works fine in Cyagenomod.

I've tried this app: WiFi Doctor, and it finally worked until I went out of the office for a few minutes. When I came back I was at square one and what's worse, WiFi Doctor couldn't cure it any longer.