Weird error on Windows 7 with RUNAS.EXE with locally defined user

The other day, I noticed something strange with Windows 7’s runas.exe command.
When I specify a local user, a local administrator for instance, I normally use the “period-notation”, like: .UserName

However, RUNAS.EXE threw an error at me: “RUNAS ERROR: Unable to acquire user password”.
Luckily, this was easily solved.

I quickly found, that if I replaced the period (.) with the computer name, the command worked as expected. See here a screenshot of the error, and the version that works.

After issuing the above command, my new Administrator window was launched nicely:

Note, that in the example above, I use shell variable %COMPUTERNAME%, as this allows you to write a small batch file that will work on any workstation regardless the name 😉