TIP: Before considering installing ASP classic on your IIS 7 server, consider how much effort it will take to convert the site to ASP.NET.
I found this question because I too was having problems getting IIS 7 to properly serve up ASP classic. After configuring a bunch of stuff to show errors, traverse parent directories, etc. I got everything working except for the data access. Just that took about 6 hours of trial and error, I was still stuck, and I got the feeling I was opening up a way to easily hack my server.
So, I decided to bite the bullet and convert my 1 mostly static ASP site to ASP.NET. That took only about 5 hours. It eliminated problems with duplicate connection strings all over the place, made deployment a snap, makes me sleep better at night knowing the server is secure, and best of all - I never have to deal with ASP classic again!