Q:

HTTP Error 500.19 Can't change IIS permisssions

The Issue
I have cloned down an exiting web forms project and when I try to build, I get the error;

HTTP Error 500.19 - Internal Server Error
  The requested page cannot be accessed because the related configuration data for the page is invalid.

Below this error, the "Detailed Error Information:" section provided a config file path that seems to point to the correct place, accept to the machine of the previous contributor of the solution.

Below is the approach I took to try resolving this issue
Initially, from this, I tried finding out where this incorrect file path is coming from but came across nothing even vaguely relative so I tried googling the error itself.
I came across this question:
How do I resolve "HTTP Error 500.19 - Internal Server Error" on IIS7.0
An answer provided by Bruce mentioned to:

"Check the directory and see if that user has appropriate rights to
  it".

In an attempt to do this, I had a quick google and same across the following question: The requested page cannot be accessed because the related configuration data for the page is invalid error
From intermension's answer, I gathered that it was "ApplicationPoolIdentity" that was not assigned the correct permissions so in ettempting to resolve this, I visited the following link. IIS7 Permissions Overview - ApplicationPoolIdentity 
I followed Jon Adams' steps successfully as shown here:

This was unsuccessful and I'm unsure of where to go now.
Thank in advance! :)

A:

You can follow there steps:

Check which application pool your website is using 

Change it to use ApplicationPoolIdentity if it is not.
Go to your website directory and search for Application Pool Identity user which has format IIS AppPool{AppPool Name} e.g. IIS AppPool\DefaultWebsite and give it read permissions

In IIS Manager select your website in the left pane and then in right pane double click the HandlerMappings icon to ensure that handlers list show up.

