Please take a look at the entity access rules.
Administration.Account can be accessed by any user. You can only edit your own record as a user.
Administration.Account is a specialization of of System.User. The Name field resides in that entity. There you have only access to your own record.
What is your goal by selecting the user by its name?
If this is part of a general process in the app, then don't directly use the User/Account data. The user/Account data should only be used to create/manage user accounts and thus login to the app by the users.
Process data should be separated. Best practice is to have an entity (Person/Member/Employee/.....) with a 1-1 association to their account.
Some earlier discussions around this topic: