SQL Server 2005 Express User Instance Madness

Hello, I'll try to make the description of this multi-problem scenario as short and sweet as possible.

First Problem
The default named instance of "SQLEXPRESS" was somehow installed on my machine and nothing can get rid of it. However, it is somehow invisible to everything else on my system, so I can't use it. How do I get rid of the instance or repair it?

Second problem
I installed another instance of the SQL Server 2005 Express and named it, "SQLEXPRESS02". I attached a database to it and successfully retrieved data from it using an application that used the following connection string:


Data Source=(local)sqlexpress02;AttachDbFilename=|DataDirectory|MyDatabase.mdf;Initial Catalog=MyDatabase;Integrated Security=True;User Instance=True

Next, I tried to use a different application to retrieve data from a copy of the same database located in a different directory and used the same connection string as that shown above. When I do this, I receive an error message similar to the following:


Database 'C:PathToMyOriginalProjectinDebugMyDatabase.mdf' already exists. Choose a different database name.

Cannot attach the file 'C:PathToMyNewProjectinDebugMyDatabase.mdf' as database 'MyDatabase'.

I then tried, out of curiosity, to change the Initial Catalog portion of the connection string to "MyDatabase2" and attempt the data retrieval again. The connection string looked like this:


Data Source=(local)sqlexpress02;AttachDbFilename=|DataDirectory|MyDatabase.mdf;Initial Catalog=MyDatabase2;Integrated Security=True;User Instance=True

Interestingly enough, it worked. However, when I switched back to the original connection string, I got the same error message as before.

What's going on here? I thought that one of the virtues of user instances was that they would attach at run-time, then disconnect when the application was through with them. If that's the case, then why am I getting errors stating that a database of the same name is already attached? Is there a way to detach these databases from a user instance? Can it be done by some value in the connection string?

Thank you in advance for your help.