I was trying to create a virtual machine for development with SharePoint 2010, but I wanted to have a full SQL Server available instead of using the standalone installation with SQL Express. Unfortunately, this situation is not supported unless you are using domain accounts. My VPC is not part of any domain, so the install won’t proceed (which is by design apparently). There is a well-documented workaround using the New-SPConfigurationDatabase PowerShell script, so I tried that. That seemed to work, it ran for a while, but then I ended up with an error:
User does not exist or is not unique
I found a post on the MSDN Forums that had the right answer. When the script prompted me for credentials, I put in a local username and password, and this was accepted. Until later when the script crashed. It turns out that I needed machinename\username and password. Even though the authentication prompt accepted the credentials without the machinename, somewhere down the line the script needed the machinename and it wasn’t there. Another important item to note was that once the PowerShell script crashed, it would no longer work even if you got all the prompts correct. I needed to exit the script shell and start again.