Server Error in '/' Application.

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Was "defense" the name of your virtual directory?

This is where it gets a bit confusing. If you configured your IIS root directory to be the DNN directory, then you do not need a virtual directory. Then, all of your portal aliases also have to match the directory path you chose.

i.e.:
Your IIS is setup to use the DNN directory as the default (root) directory of your webserver...
The domain you use should be "www.domain.com", and your portal alias should be "www.domain.com".

If you use a virtual directory "defense" instead, and have your default (root) directory in IIS as a different path...
The domain you use should be "www.domain.com/defense", and your portal alias should be "www.domain.com/defense".

You do not NEED virtual directories to use DNN (especially if you run multiple portals), but you also have to make sure your IIS settings and DNN portal alias settings match. If you need to use them because of your IIS setup, then you have problems with multiple portals because then ALL of your portals need to include that virtual directory in the alias path name.

It gets quite confusing when you do it that way, which is why I don't recommend it.