MAY 2015 - Major login issues. Anyone else getting this?

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Just upgraded one of our sites to May 2015 and several agents reported they cannot login while receiving a message that their username/password is incorrect or their account has been disabled. We've confirmed usernames are correct and accounts are fine.

From what we can tell it's somehow related to profiles where some work and others don't. Have no idea how that's causing the problem but it's really wreaking havoc within our support center. I don't suppose anyone else has had this issue (probably unlikely since we're probably one of the first sites to cut over to May 2015).