Did you check that:
Export to datasmith is in the datasmith tab in the ribbon.
There is also an issue with Datasmith not appearing in ribbon of non English version of 3dsmax, this is fixed for 5.1.1
Did you check that:
Export to datasmith is in the datasmith tab in the ribbon.
There is also an issue with Datasmith not appearing in ribbon of non English version of 3dsmax, this is fixed for 5.1.1