Hi: The only thing I see that is different than the sample on the IP Team Blog is your quotes -- you are using single quotes around your concat, and double around your ".."
Perhaps give this a try: eval(eval(ReassignRepSec, "concat(my: ReassignAnalystName, ';')"), ".."), using the Insert Field or Group button to select the ReassignRepSpec field? Not sure why that would make a difference, but it seems worth a shot....