I got this error and was pretty much clueless. It is under Windows Server 2012 and it didn’t occur in 2008
HTTP Error 500.19 - Internal Server Error
The requested page cannot be accessed because the related configuration data for the page is invalid.
Detailed Error Information:
Module IIS Web Core
Handler Not yet determined
Error Code 0x80070021
Config Error This configuration section cannot be used at this path. This happens when the section is locked at a parent level. Locking is either by default (overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny" or the legacy allowOverride="false".
Config File \\?\C:\myapp\web.config
Requested URL https://localhost:443/api/v1/Login
Physical Path C:\myapp\api\v1\login
Logon Method Not yet determined
Logon User Not yet determined
90: < /modules >
91: < handlers >
92: < remove name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" / >
This error occurs when there is a problem reading the configuration file for the Web server or Web application. In some cases, the event logs may contain more information about what caused this error.
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How did I solve it?
And then do the following in a command prompt, if required. Update to Allow on the handlers and modules section in C:\Windows\System32\inetsrv\config\applicationHost.config and remember to open as administrator
< section name="handlers" overrideModeDefault="Allow" / >
< section name="modules" allowDefinition="MachineToApplication" overrideModeDefault="Allow" / >