Solved the following dotDefender error:

Error text:
An error occured.

Action: get_update_best_practice_rules_configuration

Exception: Invalid Response

Internet Information Services 7.5

Error Summary
HTTP Error 403.18 – Forbidden

The specified request cannot be processed in the application pool that is configured for this resource on the Web server.

Detailed Error Information

Module
IIS Web Core

Notification
BeginRequest

Handler
StaticFile

Error Code
0x00000000

Requested URL
http://127.0.0.1:80/Rejected-By-UrlScan?~/dotDefender/dotDefenderWS.exe

Physical Path
C:\inetpub\wwwroot\Rejected-By-UrlScan

Most likely causes: •An ISAPI filter or custom module changed the URL to run in a different application pool than the original URL.
•An ISAPI extension (or custom module) used ExecuteURL (or ExecuteRequest) to run in a different application pool than the original URL.
•You have a custom error page that is located in one application pool but is referenced by a Web site in another application pool. When the URL is processed, it is determined by IIS that that it should have been processed in the first application pool, not the other pool.
•The Web site has multiple applications configured. The application this request is configured to run in is set to run in an application pool that does not exist.

Things you can try: •If you have an application that is trying to process a URL in another application pool (such as trying to process a custom error), ensure that they both run in the same application pool if appropriate.
•If you are trying to process a custom error URL that is located in another application pool, enable the custom errors Redirect feature.
•Verify that the application pool for the application exists.
•Create a tracing rule to track failed requests for this HTTP status code and see if ExecuteURL is being called. For more information about creating a tracing rule for failed requests, click here.

Links and More InformationThis error occurs if the application pool for the request does not exist, or if an ISAPI filter, ISAPI extension or HTTP module calls the ExecuteURL server support function (or ExecuteRequest) with a URL that is configured in a different application pool. Due to security reasons, a Web site in one application pool cannot make ExecuteURL requests against a URL in another application pool. If you have an application that is trying to process a URL in another application pool, ensure that they both run in the same application pool if appropriate.
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Screen shot:

Resolve:
I went to the ISAPI Filters for the site, saw the following:
UrlScan 3.1
C:\Windows\system32\inetsrv\urlscan\urlscan.dll
Local

Removed it, site specific, and was then able to browse to the admin section as expected.

UPDATE!!!

I found a better way to fix the issue.  Create an exclusion for dotDefender within URLScan, just like the installation instructions for dotDefender lists (http://www.applicure.com/downloads/5.11/dD-installation-guide-v5%2011_IIS.pdf), odd I know.

The file is found here:
%WINDIR%\System32\Inetsrv\URLscan
And is named
UrlScan.ini

Find the section for [AlwaysAllowedUrls] and add this line below it and above the following section:
/dotDefender/dotDefenderWS.exe ; Don’t filter requests to dotDefender

My config now has the follwoing section:
~~~~~~~~~
[AlwaysAllowedUrls]
;
; URLs listed here will always be explicitly allowed by UrlScan
; and will bypass all UrlScan checks. URLs must be listed
; with a leading ‘/’ character. For example:
;
; /SampleURL.htm
;
/dotDefender/dotDefenderWS.exe ; Don’t filter requests to dotDefender
~~~~~~~~~