"not subscriptable" should be a bit more understandable than "unsubscriptable".
diff --git a/Objects/abstract.c b/Objects/abstract.c
index e26e057..cd14386 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -153,7 +153,7 @@
 					  "be integer, not '%.200s'", key);
 	}
 
-	return type_error("'%.200s' object is unsubscriptable", o);
+	return type_error("'%.200s' object is not subscriptable", o);
 }
 
 int