I was trying to install an application and received error message:
Non root user account with UID 0.
Maybe I caused this error because when I found that I had a guest account I tried to remove it by deleting all the objects that were associated with this account. The guest account wasn't removed, and it was associated with UID 0.
MacBook Pro (Retina, 15-inch, Mid 2014), OS X Yosemite (10.10.5)