I'm playing Pokemon Emerald and when I releases Lotad, the game refuses and said it came back and was worried about the player. What's happening?
In the core series Pokémon games, Pokémon can be released using the Pokémon Storage System. However, a Pokémon cannot be released if it is the only Pokémon in the player's party. Once the Pokémon is released, it is removed from the player's possession and cannot be encountered again. In Generation III and Generation IV, if the player attempts to release a Pokémon that is the only Pokémon in their party or PC that knows a certain HM move, it will immediately return. In Generation III, these moves are Surf and Dive. In Generation IV, they are Surf, Waterfall, and Rock Climb, as well as Fly in HeartGold and SoulSilver. In Pokémon Yellow, the starter Pikachu will refuse to be released by its original Trainer. -Bulbapedia
Also, a Pokemon might not be able to be released if you have too few Pokemon. These are my only explanations.
Okay, here's what I could find:
That happens when that's the only Pokemon you have that knows a given HM. Teach whatever HMs it has to another Pokemon, then try releasing it again. (GameFAQs)
In Generation III and Generation IV, if the player attempts to release a Pokémon that is the only Pokémon in their party or PC that knows a certain HM move, it will immediately return. In Generation III, these moves are Surf and Dive. In Generation IV, they are Surf, Waterfall, and Rock Climb, as well as Fly in HeartGold and SoulSilver. (Bulbapedia)
Does Lotad know and HM like Surf? If so, try teaching Surf to another Pokémon and then releasing Lotad.
When a Pokemon has Max Happiness, it will not leave it's trainer. (A similar question on the DB)
If your Lotad has maximum happiness, it won't leave. Although, being only a Lotad, I assume it won't have max happiness unless you've had it with you for a long time.
I hope this helps!