The cause of this is, as madhavan said, is IIS will "flow" IIS settings through to sub folders/applications. I'm assuming you have your new application/virtual folder in a different location outside of the SolarWinds directory. If that's the case, you can use the following in the web.config to clear all the imported modules:
<configuration> <system.webServer> <modules> <clear /> </modules> </system.webServer></configuration>
This goes in the web.config in the folder you have created. This will clear out all the modules. You may have to go back and add some of the defaults for .NET, but it depends on what you are doing. If you do need to use the modules from SolarWinds, you have to change how the directories are setup, and not set IIS to treat your sub-folder as an application.
As for passing the username to your application, that I cannot tell you. I'm not sure there is an obvious way.
