null reference exception stack
<p>Can any one explain this exception?</p>

<p>Server Error in '/eims_web' Application:</p>

<pre><code>Object reference not set to an instance of an object. 
</code></pre>

<p>Description: </p>

<pre><code>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. 
</code></pre>

<p>Exception Details:</p>

<pre><code>System.NullReferenceException: Object reference not set to an instance of an object.
</code></pre>

<p>Source Error: </p>

<pre><code>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.  
</code></pre>

<p>Stack Trace: </p>

<pre><code>[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&amp; dataCacheDependency, CacheDependency&amp; 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.PreRenderRecursiveInternal() +322
   System.Web.UI.Control.PreRenderRecursiveInternal() +322
   System.Web.UI.Control.PreRenderRecursiveInternal() +322
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4837
</code></pre>
