Am 16.02.2014 um 12:09 schrieb Troy Henderson <thenders@gmail.com>:

> 
> Can you show the content of your file foo.tex.
> 
> 
> \starttext
> Hello World
> \stoptext
> 
> but it does this for ALL ConTeXt source files that I try to build (even ones that have built fine in the past).

Have you tried using source to run the setuptex script, e.g.

    cd <working directory for foo.tex>
    source . /opt/context/tex/setuptex
    context foo.tex

Wolfgang