We are provided two parts to use for Activation: e-mail address and a Key.
For activation, rather than type, I used Copy-Paste. I copied my e-mail address, pasted it in, then went to get the key. I noticed that when I switched back, whatever I had entered previously was gone. I made sure the key was entered, then typed my e-mail address to get the activation to work. This is the first time I have seen a dialog work like this.
If you think the activation key is invalid, it may be disappearing on you. Make sure you have both fields filled without switching away.