I was deploying an MVC5 application on a web space of the italian provider Aruba.

After launching the application I obtained the following error:

Server Error in ‘/’ Application.
Security Exception
Description: The application attempted to perform an operation not allowed by the security policy. To grant this application the required permission please contact your system administrator or change the application’s trust level in the configuration file.

Exception Details: System.Security.SecurityException: Request failed

……

And here is the screenshot:

 

 

 

 

 

 

 

I checked the web.config and found that the problem was the “system.codedom” node.

<system.codedom>
     <compilers>......</compilers>
</system.codedom>

After complete removal of the node, the application started working!