The SLAMM salinity module is somewhat woefully underdocumented. This is partially on purpose as it is somewhat experimental in nature. However, we have more faith in the model after having recently successfully calibrated it to spatial salinity data in all five major Georgia estuaries. Nonetheless it remains a "steady-state" salinity module and not a hydrodynamic model which is the consensus state of the art.
There are many additional data requirements as well as a requirement to carefully define the geometry of the salt wedge. A "classic salt wedge" estuary is required for the model to be valid. You need bathymetry data for all water sources in the model domain. I bet that's the reason for your NODATA responses.
If you are still interested in trying to apply the model after all those caveats, I'll try to start to work up a rough users manual for its implementation.
We have also recently developed multiple linkages to external salinity models (one linkage by raster maps and one by river mile) so that may also be an option for your project if you want to apply a more general and typical salinity model.