Maybe you are waiting for a mail about UU Solis and your personal id, but you haven't got it yet?
It is possible that you are waiting in vain, because you have a solis-id already that you are not aware of. If you were ever registered at the UU before, for instance for a subsidiary subject with a so-called F-studentnumber, or because you applied but then decided to withdraw your application, then your former solis-id has been activated. If you do not know your id or password, please contact Studentenservice in the Bestuursgebouw at the Uithof. They can reset your account only when you appear during office hours with an identity card.
(The UU solis-services website is not available in English).