هنگام استفاده از کنترل های Ajax Control Toolkit در صفحه با پیغام خطای :

Server Error in '/WebApplication4' Application.

Security Exception

Description: The application attempted to perform an operation not allowed by the security policy.  To grant this application the required permission please contact your system administrator or change the application's trust level in the configuration file.

Exception Details: System.Security.SecurityException: Request for the permission of type 'System.Web.AspNetHostingPermission, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
 

[SecurityException: Request for the permission of type 'System.Web.AspNetHostingPermission, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.]
   System.Reflection.Assembly._GetType(String name, Boolean throwOnError, Boolean ignoreCase) +0
   System.Web.UI.NamespaceTagNameToTypeMapper.GetControlType(String tagName, IDictionary attribs, Boolean throwOnError) +98
   System.Web.UI.NamespaceTagNameToTypeMapper.System.Web.UI.ITagNameToTypeMapper.GetControlType(String tagName, IDictionary attribs) +11
   System.Web.UI.TagPrefixTagNameToTypeMapper.System.Web.UI.ITagNameToTypeMapper.GetControlType(String tagName, IDictionary attribs) +127
   System.Web.UI.MainTagNameToTypeMapper.GetControlType2(String tagName, IDictionary attribs, Boolean fAllowHtmlTags) +228
   System.Web.UI.MainTagNameToTypeMapper.GetControlType(String tagName, IDictionary attribs, Boolean fAllowHtmlTags) +28
   System.Web.UI.RootBuilder.GetChildControlType(String tagName, IDictionary attribs) +20
   System.Web.UI.ControlBuilder.CreateChildBuilder(String filter, String tagName, IDictionary attribs, TemplateParser parser, ControlBuilder parentBuilder, String id, Int32 line, VirtualPath virtualPath, Type& childType, Boolean defaultProperty) +69
   System.Web.UI.TemplateParser.ProcessBeginTag(Match match, String inputText) +526
   System.Web.UI.TemplateParser.ParseStringInternal(String text, Encoding fileEncoding) +926

Version Information: Microsoft .NET Framework Version:2.0.50727.4927; ASP.NET Version:2.0.50727.4927

روبرو می شوم و از دات نت 3.5 هم استفاده می کنم .

با تشکر