[NTG-context] new lua error (latest beta)

I have a number of docs that have processed properly until the latest beta. Now I get this complaint in each very early in the processing: lua error > lua error on line 39 in file xxxxxxx: ...eXt/tex/texmf-context/tex/context/base/mkiv/strc-not.lua:324: attempt to index field '' (a nil value) stack traceback: ...eXt/tex/texmf-context/tex/context/base/mkiv/strc-not.lua:324: in function 'action1' [string "..."]:6: in function <[string "..."]:5> (...tail calls...) Is this a bug or has there been some change in ConTeXt coding that I need to address? Alan