I was trying to vote for someone on the Giveaway today, and I entered the name "XxISAAC_xX" into it. It said it was an invalid username. So I  tried again, copying and pasting his name into it. Still said invalid. I tried several times after that, but it never worked :L

I too, have the same problem.

I wasn't aware you could have underscores in your username when I created the giveaways. It's been fixed now, thanks for notifying me.