Can't connect to database when install DNN 6.0.1

I have downloaded DNN 6.0.1 to install on m开发者_C百科y localhost. The environment is Win7+IIS7.5+SQL 2008 Express. I have add modify permission for NETWORK SERVICE on the folder. When I use the DefaultAppPool(.NET framework 4.0), the website doesn't work, while using ASP.NET v2.0 classic, the website works but when setting up database in stallation, there goes:

Connection Error(s): Index #: 0 Source: .Net SqlClient Data Provider Class: 13 Number: 18456 Message: the Message item is blank.

So anybody know why and how solve this problem?

Thank, Sean

Make sure the app pool is running under the Network Servcie as well and that you have the proper database passwords etc.