Reproducible. Use the tag [blockquote type="cite"] (with angle brackets, of course). It's the "type" modifier that blows it up. Plain [blockquote] works.

===

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.iwethey.filter.FilterException: Handler stack is empty.
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:488)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:441)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
sun.reflect.GeneratedMethodAccessor60.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:585)
org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:244)
java.security.AccessController.doPrivileged(Native Method)
javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:276)
org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:162)

root cause

org.iwethey.filter.FilterException: Handler stack is empty.
org.iwethey.filter.FilterContext.popHandlerEntry(FilterContext.java:222)
org.iwethey.filter.AbstractMatchingPoppingHandler.process(AbstractMatchingPoppingHandler.java:55)
org.iwethey.filter.FilterContext.filter(FilterContext.java:103)
org.iwethey.filter.Filter.filter(Filter.java:94)
org.iwethey.forums.web.post.PostValidator.validate(PostValidator.java:132)
org.springframework.validation.ValidationUtils.invokeValidator(ValidationUtils.java:63)
org.springframework.web.servlet.mvc.BaseCommandController.bindAndValidate(BaseCommandController.java:373)
org.springframework.web.servlet.mvc.AbstractFormController.handleRequestInternal(AbstractFormController.java:263)
org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:153)
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:48)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:859)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:793)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:476)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:441)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
sun.reflect.GeneratedMethodAccessor60.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:585)
org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:244)
java.security.AccessController.doPrivileged(Native Method)
javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:276)
org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:162)

note The full stack trace of the root cause is available in the Apache Tomcat/5.5 logs.