Hi,

I have a web part which dynamicaly loads an ascx control. If I
configure my sharepoint for full trust, everything works fine. Using
other security settings, I get the following exception:

[SecurityException: Request failed.]
  System.Reflection.MethodBase.PerformSecurityCheck(Object obj,
RuntimeMethodHandle method, IntPtr parent, UInt32 invocationFlags) +0
  System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean
skipVisibilityChecks, Boolean fillCache) +189
  System.Activator.CreateInstance(Type type, Boolean nonPublic) +66
  System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr,
Binder binder, Object[] args, CultureInfo culture, Object[]
activationAttributes) +1036
  System.Activator.CreateInstance(Type type, BindingFlags bindingAttr,
Binder binder, Object[] args, CultureInfo culture, Object[]
activationAttributes) +114
  System.Web.HttpRuntime.CreateNonPublicInstance(Type type, Object[]
args) +40
  System.Web.Configuration.PagesSection.CreateControlTypeFilter()
+3368024
  System.Web.UI.TemplateParser.ProcessConfigSettings() +179
  System.Web.UI.TemplateControlParser.ProcessConfigSettings() +15
  System.Web.UI.UserControlParser.ProcessConfigSettings() +9
  System.Web.UI.TemplateParser.PrepareParse() +415
  System.Web.UI.TemplateParser.Parse() +155

System.Web.Compilation.BaseTemplateBuildProvider.get_CodeCompilerType()
+105

System.Web.Compilation.BuildProvider.GetCompilerTypeFromBuildProvider(BuildProvider
buildProvider) +54

System.Web.Compilation.BuildProvidersCompiler.ProcessBuildProviders()
+256
  System.Web.Compilation.BuildProvidersCompiler.PerformBuild() +29
  System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath
virtualPath) +279

System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath
virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean
allowBuildInPrecompile) +580

System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext
context, VirtualPath virtualPath, Boolean noBuild, Boolean
allowCrossApp, Boolean allowBuildInPrecompile) +93
  System.Web.UI.TemplateControl.LoadControl(VirtualPath virtualPath)
+76
  System.Web.UI.TemplateControl.LoadControl(String virtualPath) +23

Using Reflector for .Net, I can look into CreateInstanceImpl and see a
check like this:

if (entry1.m_ctor != null)
{
 if (!skipVisibilityChecks && entry1.m_bNeedSecurityCheck)
 {
   MethodBase.PerformSecurityCheck(obj1, entry1.m_hCtorMethodHandle,
     this.TypeHandle.Value, 0x10000000);
 }
}

Any hint why this check could fail or how to figure out what's the
reason is? I'm working on a custom trust file but have no idea what
permission my code might be missing.

regards,
Achim