I'm playing Red right now, and in Gen 1 I've noticed that sometimes when you use a stat move or something like that it sometimes says "It didn't affect the foe's (Pokemon name)" or something like that. Why is that?
The "no effect" message triggers when the AI hits a 25% chance to miss a stat-lowering status move like Growl or Tail Whip. This only occurs in Generations I and II.
In the Generation I and II core series games, when an in-game opponent outside of the Battle Tower uses a status move that would decrease one of the target's stats, that move has a 25% chance to fail in addition to its normal chance to miss.
Status move (Bulbapedia)
The only reason I could see why this would happen is the following:
EDIT: Speed Freak had the same problem here and some answered saying it may of been a glitch.
If its none of these then i'm not sure :/