Alternate Accounts when looging on to a specific server

Well, what I was doing was logging into a friend's account to fix something on an online server. We have 2 computers, and I tried logging into the other one. It said 'Too many alternate Accounts!'. I tried the computer I was on. same error. Then I went back to my main account (not my friend's) and guess what? The same error. The people who have logged in on this computer were: Kyle_and_alec, SirFroggy4, ClutchLego, and Newfie190. Not one of these people were on the server when me, Newfie190, tried to join. I don't think there's a way to reproduce this quickly. If there's another report on this, i'm truly sorry for making this. Thanks for your time.