I actually disagree.

this looks very nice

Sorry, I seemed to have missed an email detailing this comment.
Your solution is close but realize that Array.map will return an array with the block executed on each element of the array!
So you should be making sure to return the sum would be a good idea.

that would only work on modern browsers..

.each will only allow 1 parameter for the block so you cannot do: numbers.each {|total, i| total += i}
You can do numbers.each { |i| total += i } but you'll need total be done in some other way.

Whenever I test my code, I get the following error: Any help would be grealty appreciated.

+': nil can't be coerced into Fixnum (TypeError) from block in sum'
from each' from sum'
from `
'

# Sum Numbers
	def sum(numbers)
	if (numbers.any?) && (numbers.each { |i| i.class != String} )
		numbers.each {|total, i| total += i}
	else
		return 0
	end
	end