Error: 'classname is null, who added this'????

Hello,

I am using Tomcat 3.2 B4 on solaris 2.6.  I have just started noticing
something odd.  Once I start Tomcat, if I recompile a servlet and then
try to access it I get the following error in the browser:

Error: 500
Location:/bio/html/Initial.html    (this could be any file/servlet I try
to access)
Internal Servlet Error:

java.liang.IllegalStateException: Can't happen - classname is null, who
added this?
  at
org.apache.tomcat.core.ServletWrapper.loadServlet(ServletWrapper.java,
Compiled Code)
  at .........

I have to stop and then restart Tomcat to avoid this error after I
recompile.

Has anyone ever seen this?

Thanks,
Peter Len