I found this to be pretty funny.

500 Servlet Exception

javax.servlet.ServletException: Class `error.aspx' was not found in classpath. 

Classes normally belong in /WEB-INF/classes. 
at com.caucho.server.http.Application.instantiateServlet(Application.java:3185) 
at com.caucho.server.http.Application.createServlet(Application.java:3093) 
at com.caucho.server.http.Application.loadServlet(Application.java:3054) 
at com.caucho.server.http.QServletConfig.loadServlet(QServletConfig.java:418) 
at com.caucho.server.http.Application.getFilterChainServlet(Application.java:2794) 
at com.caucho.server.http.Application.buildFilterChain(Application.java:2750) 
at com.caucho.server.http.Invocation.service(Invocation.java:310) 
at com.caucho.server.http.RunnerRequest.handleRequest(RunnerRequest.java:342) 
at com.caucho.server.http.RunnerRequest.handleConnection(RunnerRequest.java:272) 
at com.caucho.server.TcpConnection.run(TcpConnection.java:137) 
at java.lang.Thread.run(Thread.java:536) 

Now, granted it's an error coming from Resin email servlet software but still, kinda ironic and funny and makes me wonder why the .aspx extension is on there. Maybe a custom 404/error page was defined with asp.net.