IsNewSession problem

gabbri

SYSTEM:
WINDOWS SERVER 2003 R2
DYNAMICS NAV 4.0 SP3
DYNAMICS NAV EMPLOYEE PORTAL 5.0
WINDOWS SHAREPOINT SERVICES 3

SYMPTOMS:
When I click on Save, Create New or Delete from Customer Card Web Part (installed with Employee Portal)

ERROR:
[SecurityException: Session timeout occured. Please reopen the current page to proceed.]
Microsoft.Navision.EmployeePortal.WebPartLibrary.DetailPart.Action_Command(Object o, CommandEventArgs e) +2778
System.Web.UI.WebControls.LinkButton.OnCommand(CommandEventArgs e) +105
System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument) +132
System.Web.UI.WebControls.LinkButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +7
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +11
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +177
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +7350
System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +213
System.Web.UI.Page.ProcessRequest() +86
System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +18
System.Web.UI.Page.ProcessRequest(HttpContext context) +49
ASP._catalogs_masterpage_defaultlayout_aspx.ProcessRequest(HttpContext context) +4
Microsoft.SharePoint.Publishing.TemplateRedirectionPage.ProcessRequest(HttpContext context) +153
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +358
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64

CODE:
public sealed class DetailPart : BasePart
…
internal override void Action_Command(object o, CommandEventArgs e)
…
if (this.Context.Session.IsNewSession)
{
throw new SecurityException(ErrorLibrary.GetError(ErrorNumber.UpdateSessionTimeout, false));
}
…

We have some problem with IsNewSession: is always true.

Any idea?