How to solve SQL Server Database File Open Error

"Failed to generate a user instance of SQL Server

due to a failure in starting the process for the

user instance. The connection will be closed."

After my fun with trying to get VS, SQL and Phone Tools all working together, I had the

following error trying to mount databases:

"Failed to generate a user instance of SQL Server due to a failure in starting the

process for the user instance. The connection will be closed."

If you get that error message, the solution that worked for me was to clear the SQL Express

user instance data store, located at:

%userprofile%\AppData\Local\Microsoft\Microsoft SQLServer

Data\SQLEXPRESS

(or full path)

C:\Users\\AppData\Local\Microsoft\Microsoft SQL ServerData\SQLEXPRESS