Login problems with SQL Express edition.

Hi,

when running my application and trying to access an SqlServer express edition DB, I encounter the folowing error:

Cannot open user default database. Login failed.

Login failed for user 'NT AUTHORITY\NETWORK SERVICE'.

Does any one know how this problem can be resolved?

It is the SQL Server that comes togather with the VS2005.

Thank you!

The problem doesnt occure when i run the application using the default web server (cassini). It only occures when I run it using IIS.

But how can i run the application on IIS and use the DB?

Thnaks.