May 05, 2015 01:38 PM|PatriceSc|LINK
So it seems you are using an enterprise grade SQL Server so I would say you are not using SQL Server Express? Assuming you are using the 2nd connection string, remove the User Instance=true part and see what happens.
If it doesn't hrelp, it seems best to show the exact connection string you are currently using as well as the error message you have (of if this is the generic ASP.NET message see the event log to see the actual message).
It's always easier to tell how to fix an issue when knowing exactly what it is.