Am 10.01.2015 um 11:40 schrieb Pablo Rodriguez <oinos@gmx.es>:

Dear list,

I get an error when compiling this minimal sample with beta from
2015.01.10 00:44:

   \setuplayout[header=,]
   \starttext
   \input zapf
   \stoptext

Is this a bug or am I missing something?

ConTeXt expects a dimension (e.g. 1cm) as argument for the header key but since this is missing here you get a error message for this:

 ! Missing number, treated as zero

Wolfgang