com.sun.mail.handlers.text_plain cannot be cast to javax.activation.DataContentHandler

I'm upgrading from ColdFusion 8 to ColdFusion 9. I have a Java class that I call from CF which reads and parses the contents of an mbox mailbox file. The class works fine with CF 8, but it's throwing an error in CF 9. The error is:

com.sun.mail.handlers.text_plain cannot be cast to javax.activation.DataContentHandler

The error is happening at the point where the Java code is calling the getContent() function from javax.mail.internet.MimeMessage. Based on the MIME type of the message, I'm casting the return value of getContent() to one of String, MimeBodyPart, or Part.

Does anyone have any ideas how to fix this?

Here's my Java function:

public String getHtmlContent(Part p) throws IOException, MessagingException {
    StringBuffer szContent = new StringBuffer();
    if ( p.isMimeType("text/plain") ) 
    {
        szContent.append( contentToHtml( (String) p.getContent() ) );           
    }
    else if ( p.isMimeType("multipart/*") ) 
    {
        Multipart multipart = (Multipart) p.getContent();
        for ( int i = 0, n = multipart.getCount(); i < n; i++ ) {
            szContent.append( getHtmlContent((MimeBodyPart) multipart.getBodyPart( i )));               
        }
    }
    else if ( p.isMimeType("message/rfc822") ) 
    {
        szContent.append( getHtmlContent( (Part) p.getContent() ));             
    }
    else 
    {
        throw new RuntimeException( "Cannot determine message content." );
    }
    return szContent.toString();
}

And here's the Java stack trace:

javax.activation.MailcapCommandMap.getDataContentHandler(MailcapCommandMap.java:581)
at javax.activation.MailcapCommandMap.createDataContentHandler(MailcapCommandMap.java:535)
at javax.activation.CommandMap.createDataContentHandler(CommandMap.java:191)
at javax.activation.DataHandler.getDataContentHandler(DataHandler.java:594)
at javax.activation.DataHandler.getContent(DataHandler.java:522)
at javax.mail.internet.MimeMessage.getContent(MimeMessage.java:1395)
at its.util.MBoxMessage.getHtmlContent(MBoxMessage.java:166)
at its.util.MBoxMessage.getHtmlContent(MBoxMessage.java:159)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at coldfusion.runtime.StructBean.invoke(StructBean.java:502)
at coldfusion.runtime.CfJspPage._invoke(CfJspPage.java:2393)
at cfmessage2ecfm263917690.runPage(\\web.shares\web\goat\cf\courses\classlist\message.cfm:216)
at coldfusion.runtime.CfJspPage.invoke(CfJspPage.java:231)
at coldfusion.tagext.lang.IncludeTag.doStartTag(IncludeTag.java:416)
at coldfusion.filter.CfincludeFilter.invoke(CfincludeFilter.java:65)
at coldfusion.filter.ApplicationFilter.invoke(ApplicationFilter.java:363)
at coldfusion.filter.MonitoringFilter.invoke(MonitoringFilter.java:40)
at coldfusion.filter.PathFilter.invoke(PathFilter.java:87)
at coldfusion.filter.ExceptionFilter.invoke(ExceptionFilter.java:70)
at coldfusion.filter.ClientScopePersistenceFilter.invoke(ClientScopePersistenceFilter.java:28)
at coldfusion.filter.BrowserFilter.invoke(BrowserFilter.java:38)
at coldfusion.filter.NoCacheFilter.invoke(NoCacheFilter.java:46)
at coldfusion.filter.GlobalsFilter.invoke(GlobalsFilter.java:38)
at coldfusion.filter.DatasourceFilter.invoke(DatasourceFilter.java:22)
at coldfusion.filter.CachingFilter.invoke(CachingFilter.java:53)
at coldfusion.CfmServlet.service(CfmServlet.java:200)
at coldfusion.bootstrap.BootstrapServlet.service(BootstrapServlet.java:89)
at jrun.servlet.FilterChain.doFilter(FilterChain.java:86)
at com.intergral.fusionreactor.filter.FusionReactorFilter.B(Unknown Source)
at com.intergral.fusionreactor.filter.FusionReactorFilter.A(Unknown Source)
at com.intergral.fusionreactor.filter.FusionReactorFilter.doFilter(Unknown Source)
at jrun.servlet.FilterChain.doFilter(FilterChain.java:94)
at coldfusion.monitor.event.MonitoringServletFilter.doFilter(MonitoringServletFilter.java:42)
at coldfusion.bootstrap.BootstrapFilter.doFilter(BootstrapFilter.java:46)
at jrun.servlet.FilterChain.doFilter(FilterChain.java:94)
at jrun.servlet.FilterChain.service(FilterChain.java:101)
at jrun.servlet.ServletInvoker.invoke(ServletInvoker.java:106)
at jrun.servlet.JRunInvokerChain.invokeNext(JRunInvokerChain.java:42)
at jrun.servlet.JRunRequestDispatcher.invoke(JRunRequestDispatcher.java:286)
at jrun.servlet.ServletEngineService.dispatch(ServletEngineService.java:543)
at jrun.servlet.jrpp.JRunProxyService.invokeRunnable(JRunProxyService.java:203)
at jrunx.scheduler.ThreadPool$DownstreamMetrics.invokeRunnable(ThreadPool.java:320)
at jrunx.scheduler.ThreadPool$ThreadThrottle.invokeRunnable(ThreadPool.java:428)
at jrunx.scheduler.ThreadPool$UpstreamMetrics.invokeRunnable(ThreadPool.java:266)
at jrunx.scheduler.WorkerThread.run(WorkerThread.java:66)

I removed the activation.jar file from CF's lib folder. The javax.activation classes are duplicated in jrun.jar, and both JAR file are in CF's classpath. It looks like the classes are newer in activation.jar, but removing them did the trick for the custom class. Hopefully nothing in CF is relying on the newer classes.