If not here's my answer.

Assuming you are using Internet Exlorer (I use both) Up on the top tool bar.

Tools
Internet Options
Content
Turn off the Autocomplete for usernames and passwords. There is also a choice for autocomplete email addresses. I'm not sure which one you are having the problem with it popping up.

I find this a great feature, especially signing on to Fantasy Sports where I might be three different people. It also remembers passwords.