I think I might have an old version of the Paclet,
Your version seems fine, I have the same:
"Version" /. PacletInformation["SemanticImport"]
(* ==> "0.0.458" *)
Try removing "SemanticImport"
from your machine and the re-run SemanticImport["ExampleData/50states.txt"]
. If you are on Windows, it should be here: C:\Users\*username*\AppData\Roaming\Mathematica\Paclets\Temporary
. Beware, AppData
is a hidden folder.