Set Field (or its companion, Set Field by Name) does not make the field active. Use Go to Field for that.
But as there isn't a "Go to Field by Name" I can't use that script step to make a generic script.
Any workaround to make a field active?
Give Object names to the fields on your layout using the Inspector.
Then use the "Go to Object" script step.
Note that each Object name needs to be unique.
Go to Object[Your Object Name Calculation]
Sort Records by Field [Ascending]
(For those following along, the Sort Records by Field  step requires FileMaker Pro 12.)
Yes.... That's exactly what I was looking for! Thank you very much
Perhaps a good feature request would be to have fields default object name the same as the field name, could save a lot of development time?