My Tomcat server is running from Eclipse. I have successfully added
the standard webapps folder to my Eclipse configuration, so I can see
the standard index pages. However, when I try to log in to the /
manager/html panel, a 500 error results.

The login prompt works correctly - if the wrong password is entered,
access is blocked with 401. This 500 error only occurs after
successful login. A stack trace is reproduced below.

exception

javax.servlet.ServletException: Error allocating a servlet instance
...

root cause

java.lang.SecurityException: Servlet of class
org.apache.catalina.manager.HTMLManagerServlet is privileged and
cannot be loaded by this web application
   
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:
525)
   
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:
102)
   
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:
263)
    org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:
844)
    org.apache.coyote.http11.Http11Protocol
$Http11ConnectionHandler.process(Http11Protocol.java:584)
    org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:
447)
    java.lang.Thread.run(Thread.java:619)

(Unfortunately I cannot run the tomcat server outside Eclipse because
that requires installing a Windows Service which I lack privileges
for.)