This can be a really strange one. I'm using SQL Server Express 2005, and also have the following connection string (inside a DotNetNuke web.config):

DatabasesEqualsELECTROMORPHS15304561Integrated Security=TrueUser Instance=True

Observe that there's no AttachDbFilename parameter - so I am unsure how SQL server even knows things to connect with. But it's hooking up to something since the website works and may be up-to-date!

I've attempted trying to find all .mdf files around the server, but can't use whatever likely candidates. The machine databases don't appear to contain any user tables.

Does anybody have idea if there's a "default" database which can be used - possibly one which does not come with an .mdf extension?

This really is clearly the reward for accepting a default configuration! I truly ought to know better but I am completely stumped here, so would appreciate any suggestions!

Possibly this can be a mention of only the SQL Server Instance so the default catalog can be used, until a particular database is recommended, possibly at run time.

See

http://msdn.microsoft.com/en-us/library/ms247257.aspx

Also make reference to: SQL Server Express User Instances and browse "How user intances work"

http://msdn.microsoft.com/en-us/library/ms254504.aspx

Make use of the following query to recognize the particular User Instances which are running underneath the default SQL server Express instance.

SELECT owning_principal_name, instance_pipe_name FROM sys.dm_os_child_instances

Connect with the information source using Sql Server Management studio (comes free with Sql Server Express with tools.) Right click on the database, and it'll demonstrate in which the files are saved.

See this part on User Instances. For AttachDbFilename, this parameter may be added at run-time or specified elsewhere. Search for App_Data folder within your application root directory.

The Database title may differ in the physical file title.
To discover the file on disk make use of the SQL Server Management Studio.

Management studio 2005
Management studio 2008