Infosys | Microsoft

Now, its something like this. During the days of .NET 1.1, an application could load the configuration nodes in App.Config or Web.Config (the section providers) under Medium Trust. Come .NET 2.0, and the Code Access level permissions required to load the various configuration settings of the config file are extended.

In the new way, Medium Trust checks a requirePermission attribute on the configuration section declaration - the section at the top of your config file.  For example,

<section name="exceptionManagement" requirePermission="false" type="MyNamespace.MyExceptionHandler, ExceptionManager"  />
<section name="logger" requirePermission="true" type="MyNamespace.MyLogger, Logger"/>

If they are declared as above then access to the "exceptionManagement" provider section is allowed but access to the "logger" section is not (under Medium Trust). By default, requirePermission is set to true, and we need to explicitly add the requirePermission="false" attribute to the element. And in the case of click-once deployment that made me stumble on this, I had to add this additional piece in App.Config to get it all going.

<system.web>                                                                                                                                                  

<trust level="Medium" originUrl=""/>                                                                                                                    </system.web>

And this thing about requirePermission doesn’t seem to be a documented fact and in fact if you add the attribute to the section element of your config file, intellisense tells you it is not a valid attribute for the element. But then, that's the way it works!