AFS open session with different index

We have Baan IV c4 SP 32.

We are using AFS to do deliveries session tdsls4120m000.

For some item we deliver using the pick list (Index2) so we changed the indexes in the session so the default index is 2 - Pick List. But for Cost Items we need to use Index1 - Sales Order and position.

I found the command stpapi.sort.by:

ret.code = stpapi.sort.by("tdsls4120m000", "1", mensaje.error)

But ret.code returns value 0.

Has anybody use this command. Or how have you solved the problem.

Regards

Patricio