This ASP.NET hosting tutorial explains how to set ASP.NET hosting trust level.
Trust levels for ASP.NET applications are defined using policy files. The trust levels are Full (default ASP.NET trust level), High, Medium, Low, and Minimal. The Full is equivalent to having full trust in the local computer. To map the full trust level to a policy file you should write the following code into the web.config file:
<trustLevel name=”Full” policyFile=”internal”/>
Most of Shared ASP.NET hosting providers do not support ASP.NET full trust, because of security reasons. If you need a full trust ASP.NET hosting then you should find a hosting provider which supports it or to get at least a VPS server where you will have full Administrator server access.