This is typically the result of a registration being tied to the account owner rather than the athlete. There are several ways this can happen however there is usually just one fix. An athlete needs to be removed, then re-added to the roster by the team or an administrator with permissions.
If you are a Team Administrator with "Full Access" or "Limited Access - HQ Tools" permissions or higher, click here for instructions on how to remove an athlete from the roster and/or here for instructions on how to add them back.
If you are the parent of the athlete, you will need to contact your team or league admin for assistance.