If the install wizard cannot save your web.config, you may have a problem with the permissions on your dnn installation folder. Check if full permission is given to IIS_IUSRS . This is not the same as the permissions you read about on the second page of your install wizard. The install wizard reports on the permissions you have on the database.

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The one-eyed in the land of the blind.

As someone else had done, I deleted the entire installation and ran the install again for the fourth time. This time there was an 'Auto' option (along with 'Custom' and 'Typical' for the configuration pages, and it installed just fine.

Don't think this posted properly so apologies if this ends up being a dupe post.

I'm getting the same error trying to install DNN. I installed via the Microsoft Web Platform Installer and also from the straight download. Same problem both ways. Also tried it a few times but with no joy in getting the auto option (as I can't get connected to the database)

Do I need to alter my web.config and where would I start, just the connection strings?

Here it is unaltered:

<connectionStrings>
    <!-- Connection String for SQL Server 2005/2008 Express -->
    <add name="SiteSqlServer" connectionString="Data Source=.\SQLExpress;Integrated Security=True;User Instance=True;AttachDBFilename=|DataDirectory|Database.mdf;" providerName="System.Data.SqlClient" />
    <!-- Connection String for SQL Server 2005/2008
    <add name="SiteSqlServer" connectionString="Server=(local);Database=DotNetNuke;uid=;pwd=;" providerName="System.Data.SqlClient" /> 
    -->
  </connectionStrings>

Thanks