[Ico-man]

Could be a number of reasons:

- using guest account (or other account without admin rights); login as admin and try to register BS.Player, also try right clicking on installation file and Run as administrator, like suggested by Tizio
- your account doesn't have rights to write in Documents and settings folder; acquire these rights from admin/owner of the computer
- you misspelled the registration key (its quite long); use ctrl+c to copy regkey from license email (withous spaces at the beggining or the end) and ctrl+v in Registration window to paste it correctly
- installation file might be corrupted; trey redownloading and reinstalling PRO from User area.