i got error message if i try to access the website client pc on the network by giving: http://server/DotNetNuke.Default.aspx

Server Error in '/DotNetNuke' Application.

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Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

[NullReferenceException: Object reference not set to an instance of an object.]
   DotNetNuke.Entities.Portals.PortalSettings.GetPortalSettings(Int32 TabId, PortalAliasInfo objPortalAliasInfo) +91
   DotNetNuke.Entities.Portals.PortalSettings..ctor(Int32 tabId, PortalAliasInfo objPortalAliasInfo) +83
   DotNetNuke.HttpModules.UrlRewriteModule.OnBeginRequest(Object s, EventArgs e) +2750
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +92
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64

 another issue from the dotnuke server (member server)

if  i use: http://localhost/DotNetNuke/Default.aspx - i got no problem all are working fine

but if i use http://server/DotNetNuke/Default.aspx - i get the same error message