Partial trust level in SP 2013

Hi,

Using SP 2013, I created a new Web App and new empty site collection.
When I reduce .Net Trust Level of the relevant site to a level lower than Full (and perform iisreset afterwards),
my SP page fails rendering and the attached error page is displayed (below).

What could be the problem ?

Thank you,

Eitan.

Error page:

Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately. 

Parser Error Message: Type 'Microsoft.SharePoint.ApplicationRuntime.SPPageParserFilter' cannot be instantiated under a partially trusted security policy (AllowPartiallyTrustedCallersAttribute is not present on the target assembly).

Line 558:      </buildProviders>
Line 559:    </compilation>Line 560:    <pages enableSessionState="true" enableViewState="true" enableViewStateMac="true" validateRequest="false" clientIDMode="AutoID" pageParserFilterType="Microsoft.SharePoint.ApplicationRuntime.SPPageParserFilter, Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" asyncTimeout="7">Line 561:      <namespaces>
Line 562:        <remove namespace="System.Web.UI.WebControls.WebParts" />