I seem to remember reports that only the temp One cards you buy in WM stores work for SCO loading - once they send you a real debit card it doesn't work any longer.
The one thing I've noticed is nothing I try works when there's a certain employee at the MC.
If it works with other employees, it seems that this one just doesn't know what they are doing? Have you tried loading genuine debit card -> discover to see if they are even doing the right TX type?