For a long time I didn't use the SharePoint Search configuration on my develop VM but last week I wanted to demo the search capabilities so I decided to (quickly!) create the Search App.... or not..
Everything configured, name, application pools etc. GO !!
--> Error !! The configuration couldn't create the databases because the [domain]\administrator didn't exist / have rights.
Being a DBA for a number of years, I quickly opened the SQL Management Studio, checked the user accounts and 'Administrator' was there (no domain prefix).
I tried to rename this account to [domain]\administrator but no luck, SQL didn't allow me to do this.
Couple of minutes later I saw there was another administrator account ! This one was called [machine name]\administrator. I renamed this account to [domain]\administrator and voila, problem solved.