When I go into configure system and set the URL for Mantis I get the following error:

HTTP status 500:
javax.servlet.ServletException: java.lang.NoClassDefFoundError: Could not initialize class org.apache.axis.deployment.wsdd.WSDDDocument
org.kohsuke.stapler.Stapler.invoke(Stapler.java:554)
org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:180)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:519)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:435)
org.kohsuke.stapler.Stapler.service(Stapler.java:123)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:94)
hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:86)
hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:47)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)
org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)

root cause

java.lang.NoClassDefFoundError: Could not initialize class org.apache.axis.deployment.wsdd.WSDDDocument
org.apache.axis.configuration.FileProvider.configureEngine(FileProvider.java:179)
org.apache.axis.AxisEngine.init(AxisEngine.java:172)
org.apache.axis.AxisEngine.<init>(AxisEngine.java:156)
org.apache.axis.client.AxisClient.<init>(AxisClient.java:52)
org.apache.axis.client.Service.getAxisClient(Service.java:104)
org.apache.axis.client.Service.<init>(Service.java:113)
hudson.plugins.mantis.soap.mantis110.MantisConnectLocator.<init>(MantisConnectLocator.java:12)
hudson.plugins.mantis.soap.mantis110.MantisSessionImpl.<init>(MantisSessionImpl.java:31)
hudson.plugins.mantis.soap.MantisSessionFactory.getSession(MantisSessionFactory.java:23)
hudson.plugins.mantis.MantisSite.createSession(MantisSite.java:151)
hudson.plugins.mantis.MantisSite.isConnect(MantisSite.java:123)
hudson.plugins.mantis.MantisProjectProperty$DescriptorImpl.doCheckLogin(MantisProjectProperty.java:176)
sun.reflect.GeneratedMethodAccessor610.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:185)
org.kohsuke.stapler.Function.bindAndInvoke(Function.java:101)
org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:54)
org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:74)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:519)
org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:180)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:519)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:435)
org.kohsuke.stapler.Stapler.service(Stapler.java:123)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:94)
hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:86)
hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:47)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)
org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)