Attempt by security transparent method 'Umbraco.Core.UmbracoApplicationBase.StartApplication(System.Object, System.EventArgs)' to access security critical method 'System.AppDomain....' failed.

I got this issue after hosting my umbraco website on GoDaddy server.

Solution

<configuration>
    <system.web>
       <trust level="Full" />
    </system.web>
</configuration>

This will fix your issue. Happy Coding :)