Problems: HTTP status 500

My Netflow was working fine but this morning it gaves me following error (after entering username/password):

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type Exception report

message

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

exception

java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 0
java.util.Vector.get(Unknown Source)
org.apache.jsp.jspui.traffic_jsp._jspService(traffic_jsp.java:166)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
com.adventnet.authentication.ContextChangeDetector.doFilter(ContextChangeDetector.java:100)
org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:75)

note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.
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I am running it under W2003 server
What could be wrong ???