IIS Error – The WebResource.axd handler must be registered in the configuration to process this request

After I installed Coldfusion 9 on an IIS 7 website I received an error on one of my ASP.NET pages saying that the WebResource.axd handler must be registered in the web.config file.  I looked in my web.config file and found out that the WebResource.axd file was ALREADY configured just as the error says:

<add path=”WebResource.axd” verb=”GET” type=”System.Web.Handlers.AssemblyResourceLoader” validate=”True” />

After some digging online, I found out that for some reason there is a conflict between coldfusion and Application Pools that are running in “Integrated” mode.  Once I changed the Application Pool for my website (cftest1 in the picture below), from “Integrated” to “Classic” Managed Pipeline Mode and recycled the application pool both my asp.net pages and my coldfusion pages started working.

NOTE:  Personally I don’t care if my application pool runs in “Classic” mode, but you may be different.  You will probably want to investigate the implications of running in Classic mode rather than Integrated.  I’m guessing that in “Classic” there is a greater chance that individual crashes could affect the entire website.  Also, if you are doing very complex CF or ASP.NET pages, there might be issues.  You might want to look into this further.