CID is an abbreviation for Chalmers IDentity. It is used to uniquely identify a person.
Your CID, in combination with your Chalmers password, are used to login to computers and systems. A CID is always written in lowercase when used.
If you receive an error message, it may mean that the password was not accepted. Try a different password. It takes time to save the password, so wait. You will either succeed or receive an error message. Do not go back to the main page, do not reload the page, and do not log in again.
https://chalmers.topdesk.net/solutions/open-knowledge-items/item/KB 0289/en/