Hello la_ripper
In your App Center console, access: Account > Primary Contact. Does the username contain any special characters or numbers? This account's First Name and Last Name fields must contain only standard ASCII/English non-numeric characters (the Username may contain numbers).
Locate this account under Users, edit it to remove any special characters or numbers from the first and last name fields, then save. Try to apply the license again, and let me know whether or not it succeeds.
Check this link:
https://www-secure.symantec.com/connect/forums/licensing-issue-3
Same issue.