The login name must meet the following requirements: It must be a SQL Identifier. It cannot be a system name, for example: ...

The login name must meet the following requirements:
It must be a SQL Identifier.
It cannot be a system name, for example:
- admin, administrator, sa, root, dbmanager, loginmanager, etc.
- Built-in database user or role like dbo, guest, public, etc. 
It cannot contain:
  - White space like spaces, tabs, or returns
  - Unicode characters
  - Nonalphabetic characters ("<>|:*?\/#;,%=)
It cannot begin with:
  - Digits (0 through 9)
  - @, $, +