Managed to successfully upgrade a Web Application from .Net Version 3 to Version 4.5 and I get the following error:-
HTTP Error 500.22 - Internal Server Error
As ASP.NET aspiration abortion setting has been detected abortion pill costs that does not apply in Integrated managed pipeline mode
Module: configurationValidationModule
Notification: BeginRequest
Handler: ExtensionlessUrlHandler-Integrated-4.0
Error Code: 0x80070032

Solution was quite simple and found it here:-
StackOverFlow - An ASP.NET setting has been detected that does not apply in Integrated managed pipeline mode
Fix:-
In web.config add the following or make sure it exists:-
<configuration>
<system.webServer>
<validation validateIntegratedModeConfiguration="false"/>
</system.webServer>
</configuration>