Runas Error: Unable to Acquire Password

There are so many things your forgot to document:

• what is your logon provider? Are you attached to a domain?
• are your running this from a UAC elevated command prompt?
• what does the real user name look like? Is it a system account?
• does the user account actually exist on your machine?
• can you logout and logon as that user from your machine?
• does that also work when you disconnect from the network?
• do you actually type this command or is it called from a .bat or script?
• "cannot enter the password", you can't type it or it doesn't like what you typed?

Serverfault.com is a good place to ask about user authentication.

Actually, I had the same problem with W7 Enterprise (connected to a domain, switching to a locally defined admin user) without UAC elevation with the command:

runas /user:.\admin cmd.exe

It did prompt me for the password.

It also worked when I changed it explicitly to:

runas /user:%COMPUTERNAME%\admin cmd.exe

I just had this issue.

runas /username:domain/user cmd failed

but

runas /username:domain\user cmd worked.

So give your slashes a check.