Unable to Start Debugging on the Web Server

Yesterday I started a migration project, moving a ASP NET 1.1 application to an ASP .NET 2.0/3.5 application.  Ok, so there was a lot of work to be done here, due to the fact that it had also been migrated from Visual SourceSafe to Team Foundation Server by one our our infrastructure teams. 

Well, you could say they completely unwired the whole application.  I had to redo all of the assembly references but I digress.  Once I got all of that working I was ready to run in debug to see if I broke anything.  I was greeted by the following message “Unable to start debugging on the web server.  The web server could not find the requested resource” see the image below.


Of course I instantly starting searching on the error to see how to fix it.  After several failed links I found an article talking about UrlScan.  I had no idea what UrlScan was or even if I had it installed.

I was able to find out that UrlScan is a security tool from Microsoft that restricts the types of HTTP requests that Internet Information Services (IIS) will process. By blocking specific HTTP requests, the UrlScan security tool helps prevent potentially harmful requests from reaching the server. To find out more about UrlScan go here.

I am not sure how this got installed on my work laptop but none the less it is there and correctly configuring UrlScan allowed my application to be debugged. So here is what I had to do to fix it.

First I followed the instructions here: How to configure URLScan to protect ASP.NET Web applications.

That got it configured to allow ASP items to be available but didn’t correct the issue so next I followed the instructions here Error: The Web Server Has Been Locked Down and Is Blocking the DEBUG Verb.

Here are the steps to follow to add the DEBUG Verb to the AllowVerbs sections of the Urlscan.ini file

To enable debugging on a Web server with URLScan installed
  1. Locate the Urlscan.ini file. Normally, you will find it in a directory that looks something like this:
  2. Create a copy of the file, and name it Urlscan.old.
  3. Open the original copy of the Urlscan.ini file using Notepad or the text editor of your choice.
  4. In Urlscan.ini, locate the [AllowVerbs] section. Add DEBUG to the [AllowVerbs] section. If you see ;DEBUG in the [AllowVerbs] section, remove the semicolon to uncomment the verb.
  5. Locate the [DenyVerbs] section. If DEBUG appears in the [DenyVerbs] section, remove it.
  6. Save the file.
  7. Restart the server or restart IIS.

This took me a few hours to track down hopefully by posting this it will be easier for others to find this solution.

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