Hi,
As others suggested first uncomment the parameter s_vbeln and try to pass the value for it.
And also i would like to add few points,
S_VBELN in the smatform is a paramater which can hold only one value,
S_VBELN in your driver program is a select-option which can hold multiple values.
So try passing the value s_vbeln-low.
If you want to pass select-option values do a little search on SCN you can find it.
Regards,
Anil.