I think your problem is that you have either your score text or the value for each kill made into a string somehow instead of an number, so when you try and add 1 point, it adds a 1 onto the end of the string, instead of mathematically adding it. Basically... string addition (concatenation): "1" + "2" = "12"; number addition: 1 + 2 = 3.
 "Space Trooper USA"){kind=icon}
 "Teh Stick Man Dies"){kind=icon}