I don't know what really happens, it seems that Net.Permissions are not recognized as System.Net.Permissions
Please edit app_code\xml\components\utils.vb and change the line 96 to
Return System.Security.SecurityManager.IsGranted(New System.Net.WebPermission(System.Net.NetworkAccess.Connect, url))
or
Return System.Security.SecurityManager.IsGranted(New WebPermission(NetworkAccess.Connect, url))
Both should work, more after I return from my vacation. It would be nice If you could post your import namespace sttings inside your web.config. I would like to compare it to my settings.