Martin Burnicki - 2012-08-23

Grepping through the ptpd sources yields that "truncated ancillary data" is reported if the MSG_CTRUNC flag is set in the header of a received message. This flag is defined in the standard socket.h header e.g. under Linux with the comment:
/* Control data lost before delivery. */

However, a Google search also returned this link:
http://us.generation-nt.com/answer/bug-567094-manpages-dev-recvmsg-2-doesnt-mention-msg-ctrunc-can-be-set-due-permissions-errors-help-169022341.html

which says the flag can eventually also be set due to a permission error, in the case above when SELinux denied passing of the file descriptor.

I don't know whether there's some security tool like SELinux under FreeBSD, but anyway this sounds like a possible reason for the error message.