A context error occurs when a goal or declaration appears in the wrong place.
There may or may not be anything wrong with the goal or declaration as such;
the point is that it is out of place. Calling multifile/1 as a goal is a
context error, as is having :-module/2 anywhere but as the first term in a
source file.
The SICStus_Error term associated with a context error is
context_error(Goal, ContextType, CommandType)