Symptoms

You cannot type @ key for the e-mail address in the Windows 8 upgrade assistant. @ key works fine in other programs like Notepad, Internet Explorer etc.

Resolution

Add English (United States) keyboard layout in you Windows Virtual Machine.

Learn about adding a keyboard layout in Windows: https://windows.microsoft.com/en-us/windows-8/add-language-keyboard

Then you will successfully type @ key in the Windows 8 upgrade assistant.

You may remove this layout and get back to your initial one since the @ key works fine in other text input fields.