When Windows is joined to Active Directory, logging on or authenticating for User Account Control with a local account requires that the username be entered in a computername\ username format. This can be inconvenient, especially if the computername is long and difficult to remember and type. Here’s an easy solution.

When prompted for the user account, simply enter the format: .\<username>

The ‘dot plus backslash’ before your username will tell Windows or UAC that you are entering a local account.