Csla4 and Net4 - ASPNET permission denied on the c

My application works beautifully when the Net version was not Net4. It continues to work perfectly if I create a new Windows 7 based server from scratch. Configure the permissions and away you go.

But (and there is always a but...), my customer has an existing server where the application does not even start when I move to Csla4 and Net4. All the permissions seem to be identical on my "clean" server and on his "legacy but upgraded" server. But the client gets a security error:

System.Security.SecurityException: Request failed.
   at System.RuntimeMethodHandle.PerformSecurityCheck(Object obj, RuntimeMethodHandleInternal method, RuntimeType parent, UInt32 invocationFlags)
   at System.RuntimeMethodHandle.PerformSecurityCheck(Object obj, IRuntimeMethodInfo method, RuntimeType parent, UInt32 invocationFlags)
   at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Reflection.ConstructorInfo.Invoke(Object[] parameters)
   at System.Configuration.TypeUtil.InvokeCtorWithReflectionPermission(ConstructorInfo ctor)
   at System.Configuration.RuntimeConfigurationRecord.RuntimeConfigurationFactory.CreateSectionImpl(RuntimeConfigurationRecord configRecord, FactoryRecord factoryRecord, SectionRecord sectionRecord, Object parentConfig, ConfigXmlReader reader)
   at System.Configuration.RuntimeConfigurationRecord.RuntimeConfigurationFactory.CreateSectionWithRestrictedPermissions(RuntimeConfigurationRecord configRecord, FactoryRecord factoryRecord, SectionRecord sectionRecord, Object parentConfig, ConfigXmlReader reader)
   at System.Configuration.RuntimeConfigurationRecord.CreateSection(Boolean inputIsTrusted, FactoryRecord factoryRecord, SectionRecord sectionRecord, Object parentConfig, ConfigXmlReader reader)
   at System.Configuration.BaseConfigurationRecord.CallCreateSection(Boolean inputIsTrusted, FactoryRecord factoryRecord, SectionRecord sectionRecord, Object parentConfig, ConfigXmlReader reader, String filename, Int32 line)
The action that failed was:
Demand
The type of the first permission that failed was:
System.Security.PermissionSet
The demand was for:
<PermissionSet class="System.Security.PermissionSet"
version="1"
Unrestricted="true"/>

The only permitted permissions were:
<PermissionSet class="System.Security.NamedPermissionSet"
version="1"
Name="Internet"
Description="Default rights given to Internet applications">
<IPermission class="System.Security.Permissions.FileDialogPermission, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
version="1"
Access="Open"/>
<IPermission class="System.Security.Permissions.IsolatedStorageFilePermission, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
version="1"
Allowed="ApplicationIsolationByUser"
UserQuota="1024000"/>
<IPermission class="System.Security.Permissions.SecurityPermission, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
version="1"
Flags="Execution"/>
<IPermission class="System.Security.Permissions.UIPermission, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
version="1"
Window="SafeTopLevelWindows"
Clipboard="OwnClipboard"/>
<IPermission class="System.Drawing.Printing.PrintingPermission, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
version="1"
Level="SafePrinting"/>
<IPermission class="System.Security.Permissions.MediaPermission, WindowsBase, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
version="1"
Audio="SafeAudio"
Video="SafeVideo"
Image="SafeImage"/>
<IPermission class="System.Security.Permissions.WebBrowserPermission, WindowsBase, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
version="1"
Level="Safe"/>
</PermissionSet>

The method that caused the failure was:
System.Object CreateSectionWithRestrictedPermissions(System.Configuration.RuntimeConfigurationRecord, System.Configuration.FactoryRecord, System.Configuration.SectionRecord, System.Object, System.Configuration.ConfigXmlReader)

I am studying the changes to ASPNET security in Net4, and am thorougly confused.

Has anyone else come across this problem and can point me in the right direction? To repeat, the application works perfectly in a remote environment which I create from scratch, but not in an updated legacy server.

I think that the server is configured for "Medium Trust" in the web.config or so. As far as i know CSLA requires "Full Trust" to clone the business objects.

If that's not the issue u can try to add the server to the client's trusted zone in the windows registory under

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap]

for more information u can browse to http://blogs.technet.com/b/heyscriptingguy/archive/2005/05/02/how-can-i-add-a-site-to-internet-explorer-s-restricted-sites-zone.aspx