[boost] [1.56.0 b1] Issue with mpl/is_convertable/asio

In testing '1.56.0 Beta 1' I have found that I am unable to compile https://github.com/splunk/pion on RHEL6_x64 Pion compiles fine with 1.55.0 I suspect the recurring "anonymous enum" is the kicker, though I am not sure where to even begin in diagnosing this. error: ‘const boost::asio::detail::buffer_sequence_adapter_base::<anonymous enum>&’ is/uses anonymous type error: no type named ‘type’ in ‘struct boost::is_convertible’ error: ‘value’ is not a member of ‘boost::mpl::aux::nested_type_wknd >’ Full error log: http://pastebin.com/yeScQCpx If I get a chance I will see if I can reproduce this on a more modern compiler. Any assistance in correcting this before the 1.56.0 release would be appreciated. It also may or may not be related to http://thread.gmane.org/gmane.comp.lib.boost.devel/253259/focus=253261 Regards, Thomas