HTTP Error 500.19 - Internal Server Error in Windows 7 IIS

When you get this error it means that there's probably something broken in your site's web.config file. IIS7 is very helpful in these cases and will usually point you roughly where the problem lies.

For example, I've deliberately broken a web.config on a test site by making it malformed XML:

The areas highlighted in red are providing me with a hint as to what is broken.

Without seeing the full error message from your site it would be hard to speculate what is wrong other than that something is invalid in your web.config file (or perhaps a parent web.config).

Update:

Based on your update and the new screenshot comment out the line indicated in red in your web.config file, e.g.:

<!-- <modules runAllManagedModulesForAllRequests="true"/> -->

It looks like this setting has been locked somewhere on your machine, probably in the applicationHost.config file in C:\Windows\System32\inetsrv\config.

You could try unlocking this setting to allow the web.config setting to be used by running the following on an Administrator command line:

appcmd.exe unlock config /section:system.webserver/modules /commit:apphost