You should leave the following tag intact on your local machine
You effectively lowered the trust level, and there is no need to do it in your local environment. So, going back to your first error message, you may have the global trust level set to low on a machine level, as it overrides the individual application settings. Global settings are defined in a config file that is located here:
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config\web.config (the location depends on the version of .NET and your Windows installation folder). Look for a trust element in that file.
It this is not the cause, we should try a TeamVIewer session to diagnose it. Do you have any other ASP.NET applications running on that server? If not, it may be caused the the IIS misconfiguration that is easily solved with the aspnet_regiis tool.