HTTP Status 500 - Apache Tomcat/5.0.28 - Error

We get this frequently:

javax.servlet.ServletException: State cookie is not passed along with the request. Can happen in case of use of back button.
com.adventnet.client.view.web.StateFilter.doFilter(StateFilter.java:51)
com.adventnet.authentication.ContextChangeDetector.doFilter(ContextChangeDetector.java:100)
org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:75)

root cause

com.adventnet.client.ClientException: State cookie is not passed along with the request. Can happen in case of use of back button.
com.adventnet.client.view.web.StateParserGenerator.processState(StateParserGenerator.java:284)
com.adventnet.client.view.web.StateFilter.doFilter(StateFilter.java:35)
com.adventnet.authentication.ContextChangeDetector.doFilter(ContextChangeDetector.java:100)
org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:75)

What is the cause?

Thanks.