Forum User can't login with correct credentials
 

I just recently upgraded to 4.x and everything is working great. However I have one user who emailed me who simply can't login. I tried logging in myself under his username and reset his password and all. And no matter what I do it tells me 'Wrong Username or Password'. I've tried manually changing his password several times and even had him do a password reset himself via the 'Forgot Password' link. I also went into AdminCP/Maintainence/Update Counters and did 'Fix Broken User Profiles' but that didn't work either. Can someone help me further?

Thanks