I am getting this Exception When I am trying to access database from C#.
My Connection String is
Data Source=(localdb)\\v11.0;integrated security=tr
LocalDB instances are all "User Instances", and there's no need to specify User Instance=true
in your connection string, in fact it is not even supported (as you can see). Just remove this part and it's going to work fine.
Just to add some more information. If some how this doesn't work for you and it still complains that its not able to locate server. You will be required to set following two attributes on your application pool identity in applicationHost file
<add name="DefaultAppPool">
<processModel identityType="NetworkService" loadUserProfile="true" setProfileEnvironment="true" />
</add>
where these two attributes are required to make sure your account can start LocalDB server.