What's the best way to troubleshoot an ASP.NET security exception?

I'm running into an error I just can't solve. I'm trying to host my website through an external hosting company.

Most reports consist of a server side permission issue but my hosting doesn't think that is the issue and won't budge on the idea.

Here is the message I'm getting:

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.

These are the suggestions I got send through from my hosting company:

Change to "On"

<customErrors mode="Off"/>

Your connection is also referencing a database called aspnet-Foundation-20151005115145.mdf however I cannot locate this file, it's likely your database connection string is incorrect as its trying to connect to a local database.

My database isn't active and is commented out in the Web.config file so this shouldn't be playing a part in the problem, right?

What's the best way to troubleshoot this issue?