It doesn't matter what version of SQL you're on, upgrading to etc...this issue can pretty much be resolved using this process (including pre-release/CTP/Beta/old-to-new etc.), although you might always be the exception :-) This took me a long time to figure out, so I hope it helps you out!
Problem/Sympton: I went to upgrade a perfectly working SQL 2008 R2 standard server (which was using a Default Instance, nothing crazy) to SQL 2012. The Setup failed halfway through with a random error connecting to SQL Analysis Services (your failure could be different)...then it indicated all I had to do was fix the problem and re-run my SQL 2012 Upgrade...this wasn't true :-)
Error/Result: I had an "orphaned SQL instance" called MSSQLServer.Inactive and no matter what I tried, I could not get this to "uninstall"
The most-recommended Resolution to the Error/Result: Your internet search will most likely lead you to attempt many things, none of which will work, and finally to the suggestion of trying to uninstall the Inactive SQL Instance using the command line
setup.exe /ACTION=uninstall /FEATURES=Feature_List /INSTANCENAME=Instance_Name
The REAL Resolution Steps: (don't bother trying to figure out what went wrong...feel free to try the most-recommended resolution first if you'd like...but I'd suggest that if you have the above error/result, do the following:
Note: to make sure the reinstall/install works smoothly, make sure you do the following:
I hope this helps!