Insufficient symbol fonts error

[Alan Bowen <acbowen@Princeton.EDU>]

I am getting some puzzling errors when I try to use the Greek fonts  
in math formulae (to represent Greek numerals as written in mss.)

In a short file, both
\overbar{\grk{kj}} and
$\overline{\hbox{\grk{kj}}}$
work as expected, even when they occur in Greek text.

But in a long, complicated file with lots of Greek etc. and  the same  
environment file, I get

! Math formula deleted: Insufficient symbol fonts.
\stopmathmode ->$

\dodounderbar ...nderbar {-\dimen 0}{\dimen 2}{#1}
                                                   \egroup
\processisolatedwords ...dwordsfalse #2{\unhbox 0}
                                                   \else  
\isolatedwordstrue \...

\redounderbar ...sisolatedwords {#2}\dodounderbar
                                                   \egroup
l.1 ...-n'o\-menoc <hmer\-~wn \overbar {\grk {kj}}
                                                    ka`i pr'wtwn  
<exhkost~wn ...

\rescanwithsetup ...\scantokens {#2\ignorespaces }
                                                   \egroup
l.81 ...wn >embol'imwn <hmer~wn d/ >ep'ages\-jai.}
                                                    [8.44] \grk 
{<'ojen o>u de...

I am note really sure what this error message means or how to deal  
with it. Any suggestions will be gratefully received.

I am running the latest ConTeXT on the latest teTeX distribution.

Best, Alan