fumbler

from WordNet (r) 3.0 (2006)

fumbler
    n 1: someone who makes mistakes because of incompetence [syn:
         {bungler}, {blunderer}, {fumbler}, {bumbler}, {stumbler},
         {sad sack}, {botcher}, {butcher}, {fuckup}]

from The Collaborative International Dictionary of English v.0.48

Fumbler \Fum"bler\, n.
   One who fumbles.
   [1913 Webster]