In processing a book that I have edited, there is no problem using
LuaMetaTeX, Version 2.00.0, 2019.07.31

But with LuaMetaTeX, Version 2.00.0, ConTeXt  ver: 2019.09.10,
the process stops in a specific chapter and quits with a fatal error:

tex error       > tex error on line 26 in file c_12-01_Greenbaum.tex: !
Undefined control sequence


\referencerealpage ->\clf_referencerealpage



\scrn_button_make_yes ...unter \referencerealpage

                                                  \relax \ifcase
\scratchcou...

\scrn_button_make ...ke_yes \scrn_button_make_nop

                                                  #1#2#3#4 {#5}\endgroup

\scrn_button_direct_indeed ...onparameter {#2}{#3}

                                                  \egroup \endgroup

l.26 ]



l.37 ]



...

l.249 ...BHA_12-01_Plate01.pdf][width=.5\textwidth]{

                                                  }

16

17     \def\ChapterSubTitle{The Hellenistic Horoscope}

18     \def\SubChapterNo{12.1}

19     \relax

20     \startBrillChapter[reference=Ch12,

21     title={\vglue6pc{\ChapterNo}~\\

22     \ChapterTitle},

23     bookmark={12 Astral Divination and Natal Astrology}]

24

25     \startBrillSubChapter[reference=DGG12-01,

26 >>  title={{\SubChapterNo}~\\

27     \ChapterSubTitle},

28     bookmark={12.1 The Hellenistic Horoscope}]

29     \byline

30     \startLevelBnHead[reference=12.1.1,

31     title=Introduction]

What puzzles me is that the relevant coding for this chapter is the same as
for several other chapters that process with no problems. It would be good
to know if this is a problem in the chapter itself that I can fix or if
there is a problem in the latest standalone.

The error-log reads:

return {
 ["filename"]="c_12-01_Greenbaum.tex",
 ["lastcontext"]="\n\\referencerealpage ->\\clf_referencerealpage \n
                     \n\\scrn_button_make_yes ->\\scratchcounter
\\referencerealpage \n                                        \\relax
\\ifcase \\scratchcounter \\expa...\n\\scrn_button_make
...\\scrn_button_make_yes \\scrn_button_make_nop \n
                         #1#2#3#4 {#5}\\endgroup
\n\\scrn_button_direct_indeed ...buttonparameter \\setbuttonparameter
{#2}{#3}\n                                                  \\egroup
\\endgroup \nl.26 ]\n     \nl.37 ]\n     \n...\nl.249
...HA_12-01_Plate01.pdf][width=.5\\textwidth]{\n
                       } ",
 ["lastluaerror"]="?",
 ["lasttexerror"]="! Undefined control sequence",
 ["lasttexhelp"]="The control sequence at the end of the top line of your
error message was never\n\\def'ed. You can just continue as I'll forget
about whatever was undefined.",
 ["linenumber"]=26,
 ["offset"]=10,
}

Alan