Is your web.config in the root directory of your application?
Have you tried just writing the value to the screen as opposed to actually trying to use it? (e.g. Response.Write(ConfigurationSettings.AppSettings("[keyname]"))
I store all of my database connection strings in the web.config file and do something like this:
<add key="Clients" value="workstation id=PC;user ID=Username;password=Password;data source=Server;persist security info=True;initial catalog=Database"/>
sqlConn = New SqlConnection
sqlConn.ConnectionString = ConfigurationSettings.AppSettings("Clients")
And this works fine.
--Stole this from a moderator
I will only tell you how to do it, not do it for you.
Unless, of course, you want to hire me to do work for you.