MIT's documentation implies the max block can accept a List Returns the largest value of a set of numbers. . After a little experimentation it seems a List is not a set of numbers.
MIT’s documentation is not what it says exactly. It “Returns the largest value of a set of numbers.” but not directly from a List because the puzzle pieces will NOT accept a List as input. 
Here is ABG's solution:
See the old AI2 Forum
-- Steve 