Hi Ti
if you already have suceed in sweeping from 0 to 25 v
it should not be a major problem to do the other sweep.
Is your supply floating or grounded !
Remember you have to enable the appropiate supply .
Also your output supply . Set the -25v supply to your negative (ground) connection
and the 25V to your positive supply connection.
If you have further queries don't hesitate.
If need be post a jpg of your working code.
xseadog