HTTP Status 500

Followign down error i get when i try to login to my page.
here my front login page is open and then when i try to login that time this error i reciving.
here my server is AIX server and TOMCAT webserver and DB2 database i m using.
Few month before this portal was working and now giving this error.
please give me any solution if u have.
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HTTP Status 500 -
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type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:372)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

root cause

java.lang.NullPointerException
validate.Validate.authenticate(Validate.java:56)
org.apache.jsp.secure_jsp._jspService(secure_jsp.java:85)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.

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Apache Tomcat/5.0.28

Kashyap143
Profile Answers by Kashyap143 Questions by Kashyap143
Jun 12th, 2008
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srinivasan_81
Profile Answers by srinivasan_81

Aug 4th, 2008

Please let us know what action are you trying to perform after login? Are you getting this error while login? Have you stored login members list and trying to retrieve them from DB and while retrieving are you getting this error? if so check up your JDBC connections and the resultset.