null reference exception stack

Can any one explain this exception?

Server Error in '/eims_web' Application:

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:

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:

[NullReferenceException: Object reference not set to an instance of an object.]
   System.Xml.XmlLoader.Load(XmlDocument doc, XmlReader reader, Boolean preserveWhitespace) +24
   System.Xml.XmlDocument.Load(XmlReader reader) +108
   System.Web.UI.WebControls.XmlDataSource.PopulateXmlDocument(XmlDocument document, CacheDependency& dataCacheDependency, CacheDependency& transformCacheDependency) +342
   System.Web.UI.WebControls.XmlDataSource.GetXmlDocument() +253
   System.Web.UI.WebControls.XmlHierarchicalDataSourceView.Select() +51
   System.Web.UI.WebControls.Menu.DataBindItem(MenuItem item) +326
   System.Web.UI.WebControls.Menu.PerformDataBinding() +99
   System.Web.UI.WebControls.HierarchicalDataBoundControl.PerformSelect() +126
   System.Web.UI.WebControls.BaseDataBoundControl.DataBind() +125
   System.Web.UI.WebControls.Menu.DataBind() +29
   System.Web.UI.WebControls.BaseDataBoundControl.EnsureDataBound() +104
   System.Web.UI.WebControls.Menu.EnsureDataBound() +70
   System.Web.UI.WebControls.BaseDataBoundControl.OnPreRender(EventArgs e) +43
   System.Web.UI.WebControls.Menu.OnPreRender(EventArgs e, Boolean registerScript) +89
   System.Web.UI.WebControls.Menu.OnPreRender(EventArgs e) +63
   System.Web.UI.Control.PreRenderRecursiveInternal() +200
   System.Web.UI.Control.PreRenderRecursiveIntern开发者_如何学Pythonal() +322
   System.Web.UI.Control.PreRenderRecursiveInternal() +322
   System.Web.UI.Control.PreRenderRecursiveInternal() +322
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4837

Without seeing your code it is going to be hard to say, but by the looks of the stack trace, I will wager a guess and say you have a TreeView/Menu bound to an XmlDataSource.

Clearly something is going wrong during the databinding process, but again without seeing your code that populates the XmlDataSource it is going to be next to impossible to assist you further.

The XmlReader instance passed from XmlDocument.Load to XmlLoader.Load is null, which means that XmlDataSource.PopulateXmlDocument passes a null reader to XmlDocument.Load, which occurs when XmlDataSource.GetReader returns null.

The only code path where this happens requires that XmlDataSource.DataFile is null or empty and XmlDataSource.Data is either null, empty or costs of only white-space characters.