How to load index.asp in IIS 7.5 - iis

Question

I have a site/application I would like to load in IIS. The root of the folders contains a web.config and index.asp. The sub folders are asp, scripts, styles, images.
I add Add Web site in IIS, define the physical path to the location of the index.asp, assign the IP address for host name I tried local host, IP, and leaving it blank. When I click on Browse Website I receive a HTTP 500 Internal Server Error. IIS is running and the Web Site is started in the Manage Website menu.
If I write a short index.html hello world page and set it as default document it displays ok. When I change default document back to index.asp I get the 500 error again.
Could someone give me a tip on how to proceed?
Here is my web.config:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.web>
<identity impersonate="true" />
</system.web>
<system.webServer>
<defaultDocument>
<files>
<add value="index.asp" />
</files>
</defaultDocument>
</system.webServer>
</configuration>

Answer 1

This is going to be a guess at best, since a 500 can mean anything without a sub-status code. It probably is due to configuration inheritance. index.asp is already in the default list of default documents at the server level. By adding index.asp, it may be causing a unique hey violation when the configuration inheritance is flattened into the effective configuration.
Suggestion:
Add a <clear /> element right above the <add value="index.asp" /> and try again. Otherwise, we will need to go get the sub status code of that 500 to get more information. The IIS log usually contains the sub status in the sc-substatus.
Resulting Configuration
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.web>
<identity impersonate="true" />
</system.web>
<system.webServer>
<defaultDocument>
<files>
<clear />
<add value="index.asp" />
</files>
</defaultDocument>
</system.webServer>
</configuration>
If this works, then the reason it originally works with index.html because index.html is not in the default files list.
Additional Note
The other thing I can think of is that impersonation being enabled. If you are running the application pool in Integrated Pipeline mode, you'll need to turn off integrated mode configuration validation. More information can be found here: Integrated Pipeline mode configuration validation.
New Resulting Configuration
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.web>
<identity impersonate="true" />
</system.web>
<system.webServer>
<validation validateIntegratedModeConfiguration="False" />
<defaultDocument>
<files>
<clear />
<add value="index.asp" />
</files>
</defaultDocument>
</system.webServer>
</configuration>