ServeletException in .jsp

If I click on a tab in our application [intern is a JSP page] I et an error saying " [ServletException in :/WEB-INF/pages/main/main.jsp] null' ".But in another instance the same jsp page doesn't give any error ,the page content will b displayed properly.

I wanted to know what all the reasons to cause this exception.

I hav also removed all th comments written in th jsp page .

Following is th JSP page code:

Code:

<%@ taglib uri="/tag/struts-html" prefix="html" %>
<%@ taglib uri="/tag/struts-logic" prefix="logic" %>
<%@ taglib uri="/tag/struts-bean" prefix="bean" %>
<%@ taglib uri="/tag/exxor" prefix="exxor" %>

<script language="javascript">
function submitSearch(id)
{
	document.searchResultSubmit.cancelSearch.value="false";
	document.searchResultSubmit.ID.value=id;
	document.searchResultSubmit.submit();
}
function validateSearch()
{
	if (document.searchSubmit.SEARCHVALUE.value.length < 2)
	{
		alert("Please enter atleast two characters for search");
		document.searchSubmit.SEARCHVALUE.focus();
		return false;
	}
	if (checkWildChar("searchSubmit", "SEARCHVALUE") == false) return false;
	return true;	
}
function cancelSearch()
{
	document.searchResultSubmit.cancelSearch.value="true";
	document.searchResultSubmit.submit();
}
</script>
<div align="center">
<%String resp=(String)session.getAttribute("RESPONSIBILITY");
 if("XXOR_CA_GMS".equalsIgnoreCase(resp))
 {%>
 	<form name="searchSubmit" onSubmit="return validateSearch()" action="<%=request.getContextPath()%>/do/garnishor/ca/vendor/search" method="post">  
 <%}
  else
 {%>
 	<form name="searchSubmit" onSubmit="return validateSearch()" action="<%=request.getContextPath()%>/do/garnishor/vendor/search" method="post">  
 <%}
%>
<input type="hidden" name="SORT_COLUMN" value="<%=request.getParameter("SORT_COLUMN") == null?"":request.getParameter("SORT_COLUMN")%>"/>
<input type="hidden" name="SORT_ORDER"  value="<%=request.getParameter("SORT_ORDER") == null?"":request.getParameter("SORT_ORDER")%>"/>
<input type="hidden" name="DATEFROM" value="<%=session.getAttribute("effectiveDate")%>" />
<input type="hidden" name="OPERATINGUNIT" value="<%=request.getParameter("OPERATINGUNIT") == null?"":request.getParameter("OPERATINGUNIT")%>"/>
<table>
	<tr>
	 <td>
		<fieldset>
		<legend style="font-weight:bolder;font-size:14px">Vendor Search</legend>		
		<table>
			<td>
				<exxor:createHTMLOptions property="SEARCHCRITERIA" scope="request" propertyId="SEARCHCRITERIA" empty="false" SQLCommand="dd-vendor-search">
				</exxor:createHTMLOptions>
			</td>
			<td>
				<input type="text" name="SEARCHVALUE" size="15" maxlength="50" value="<%=request.getParameter("SEARCHVALUE") == null?"":request.getParameter("SEARCHVALUE")%>"/>
			</td>
			<td>
				<input type="submit" value="Search"/>
			</td>
			<td>
				<input type="button" value="Cancel" onClick="javascript:cancelSearch();"/>
			</td>
			</tr>
		</table>
		</fieldset>
		</td>
	</tr>
</table>
<input type="hidden" name="redirectURL" value="<%=request.getParameter("redirectURL")%>">
</form>
<script language="javascript">setFocus("searchSubmit", "SEARCHVALUE");</script>
<%if("XXOR_CA_GMS".equalsIgnoreCase(resp))
 {%>
 	<form name="searchResultSubmit"  action="<%=request.getContextPath()%>/do/garnishor/ca/vendor/search/submit" method="post">  
 <%}
  else
 {%>
 	<form name="searchResultSubmit"  action="<%=request.getContextPath()%>/do/garnishor/vendor/search/submit" method="post">  
 <%}
%>
	<input type="hidden" name="ID" />
	<input type="hidden" name="cancelSearch" />
	<input type="hidden" name="redirectURL" value="<%=request.getParameter("redirectURL")%>">
	<input type="hidden" name="OPERATINGUNIT" value="<%=request.getParameter("OPERATINGUNIT") == null?"":request.getParameter("OPERATINGUNIT")%>"/> 
</form>
<% if (request.getParameter("SEARCHCRITERIA") != null && request.getParameter("SEARCHCRITERIA").length() > 0)
	{
%>
<exxor:transformer SQLCommand="sr-vendor" XSL="DBSearchList.xsl">
	<exxor:param name="form-name">searchSubmit</exxor:param>
	<exxor:param name="sort-column"><%=request.getParameter("SORT_COLUMN")%></exxor:param>
	<exxor:param name="sort-order"><%=request.getParameter("SORT_ORDER")%></exxor:param>
</exxor:transformer>
<%
	}
%>
</div>