In order for this to work, you have to clear cache and cookies in your browser FIRST. Once you do this, you also need to close and restart your browser. Changes won't take place until you do, so the browser will think the old cookies are still active.
Checked your password, and the next step is to reset it (it doesn't meet the requirements). Do that here. Make sure that when you make your new password, it contains letters and numbers only and is 8 or more characters in length.
Then, you need to follow the steps to activate.
A common mistake is entering the birthday information incorrectly, which means activation will not proceed. It MUST be entered in this format: YYYY-MM-DD. You MUST use dashes in between the numbers, or it will not accept your input.
Another thing which commonly happens is a user inputs a space in to the pen name. As that is no longer allowed, if you want a separator, use a dash or underscore.