I have been processing a number of files using the same environment file. Each time, early in the log file I get the very same message:

...

(/usr/local/teTeX/share/texmf.local/tex/context/base/pdfr-ec.tex)

Overfull \hbox (13.2pt too wide) detected at line 63

[]

system : module ancientgreek loaded

(/Users/acbowen/Library/texmf/tex/context/third/greek/t-ancientgreek.tex

loading : module ancientgreek

...

The problem is that I can see no evidence in the document of an overfull \hbox. Moreover, if I change the font from SIL-Gentium to Latin Modern, the message goes away, though it returns once more if I use GFSDidot say (only the line number differs).

Can anyone explain what is happening or suggest how I may proceed to determine what is happening and why?

Alan