Class of 2026 here, it seems like the welcome reception event register method no longer works this year, but for the CalNet ID thing I have some friends saying they see forbidden and some others saying they see not authorized.
According to what I remember from my own experience from last year, once you are admitted, you have to log into CalCentral using your MAP@Berkeley ID in order to set up your CalNet ID (kind of like a username for all your student accounts and your berkeley.edu email), only after that can you accept your offer on CalCentral. Our offers came out on March 24th, but afterwards I saw on CalCentral that some of the new admitted student tasks such as “accept offer of admission” are “assigned Mar 20th”, which indicates that the school may have already set up every admittee’s account before the release of the decisions.
I am not the expert on HTTP but I have some CS friends who said 401 not authorized is different from 403 forbidden in the sense that for “not authorized”, it means that the user provided incorrect/nonexistent credentials, and for “forbidden” it means the credentials are authenticated but the user doesn’t have the authorization to view the page requested.
Combining these two bits of information we can postulate that it is likely that they have set up accounts in the CalCentral database for those who are admitted, but they are forbidding them to access the page as of now (403). Those who are rejected/waitlisted do not have an account created in the server, so they get 401.
Highly probabilistic predictions here, what I said should not be taken to be 100% true.