I am having problems with the CalculateSimpleRoute method, I keep getting the following error:

PHP Code:

    [faultcode] => soap:Client
    [faultstring] => Server was unable to read request. --> There is an error in XML document (1, 444). --> '' is not a valid value for SegmentPreference.
    [detail] => 


It seems as though passing "Quickest" as a string is not working. I'm passing it as a string, because using the example provided here: Consuming MapPoint Web Service in PHP

they substitute a string ("AddressFlag LatLongFlag") instead of an actual FindResultObject (enumeration).

I tried the same technique for SegmentPreference, but its not working. Any tips?