odd forbidden errors

I have an install where the user was trying some plugins then all the sudden he could not login, after entering the name and pw, he got a blank page with the word forbidden on it. He can login from a different location but not at his house. I have no problems logging in with his user info and mine. he cannot with anyones name and pw including mine. I tried deleting his user profile and making a new on, same thing. I removed all his plugins and still the same problem. I asked him to restart and/or check the settings on his router. Any ideas of what I can check now? I had him try to login to another of my sites on my host (wp 3-6 also) and he cannot. I had him log into another site I have on a different host, got in no problem.