Debugging is not supported under current trust level settings

When you try to open any web service/web-application from Visual Studio, you may get the following error:

Debugging is not supported under current trust level settings.

The problem is with the trust level setting of your application. Modifying the web.config file of your application would solve this problem:

Solution:
Locate the <system.web> section.
Insert the tag: <trust level="Full" />