Swift Exec_I386

I am getting a really strange error on the first line of this block of code, which is part of an internal function to find the median of 3 in a quicksort:

if( arr[left] > arr[center] ){
        var temp = arr[center]
        arr.removeAtIndex(center)
        arr.insert( arr[left], atIndex: center)
        arr.removeAtIndex(left)
        arr.insert(temp, atIndex: left)
    }

The EXEC code is I386. The strange thing is that the if statement above this one (which is very identical except with slightly different left, right, center arguments) works flawlessly.