Error after recompiling servlet code

[Tualha Khan]

Dear All,
Hey,
Some times (and not everytime, just some times) I get the following error when I re-compile my
servlet code and access it using a web browser.
I do not restart tomcat after re-compiling. I get this error when I am just trying to open the
html page which will ultimately call the servlet. However, after restarting tomcat, everything
works fine again. Why?

=================================================
Error: 500
Location: /vsnlform.html
Internal Servlet Error:
java.lang.IllegalStateException: Can't happen - classname is null, who added this ?
at org.apache.tomcat.core.ServletWrapper.loadServlet(ServletWrapper.java:261)
at org.apache.tomcat.core.ServletWrapper.init(ServletWrapper.java:289)
at org.apache.tomcat.core.Handler.service(Handler.java:254)
at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
at org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:797)
at org.apache.tomcat.core.ContextManager.service(ContextManager.java:743)
at
org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java
:210)
at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java, Compiled Code)
at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java, Compiled Code)
at java.lang.Thread.run(Thread.java:479)
===============================================
Thanks a lot.
Bye,
Tualha Khan