We like to discuss an issue, which normally happens to ASP.NET 4.5 website on Windows Server 2008. We did not spot this issue on Windows Server 2008/Windows Server 2012 and we believe that this issue happens to ASP.NET 4.5 Framework on Windows Server 2008 only. Please note that ASP.NET 4.5 is not supported on Windows Server 2003 or lower.

When you are using Windows Server 2008 and you do make an upgrade of ASP.NET framework to ASP.NET 4.5, your site can stop working with the error message: “Operation could destabilize the runtime”

The following is the detail of the error message:

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.  

Exception Details: System.Security.VerificationException: Operation could destabilize the runtime.

To resolve this issue, please kindly make sure the following items are set on your IIS:

1. Please make sure that the ISAPI Filters of your website is set to Revert to Inherited
2. Please make sure that the application pool is running under ASP.NET 4.0 (ASP.NET 4.5 and ASP.NET 4.0 will share the same application pool settings)
3. Please make sure the “Enable 32-bits mode” is set to False

If you are looking to host your ASP.NET 4.5 website on Windows Server 2012, please have a look at asphostcentral.com

Hope this helps!