But there was no target... ?

I've noticed that some moves give out the message "but there was no target..." when used. What is causing this? Is it an error or is it similar to missing/evasion under different mechanics? I've only noticed this in Nuclear pokemon so far so I also suspect that it has something to do with ignoring orders. Still, I don't want to keep guessing and I wanna get a reliable answer.

I think, it is somehow connected with the types of your attack and your enemy. For example, you can't use Leech Seed on other Grass types because it doesn't make sense that they get hurt.

But it doesn't always happen with that specific move. One of the moves in question that I can remember was Radioacid and I used it on a regular Costraw. Besides, using a move which the enemy pokemon is immune to gives the reply "It doesn't affect foe/wild [pokemon name]".

Thanks for this, I vaguely remember something of the sort also with using Nuclear Pokemon though I've forgotten the exact details. I'll keep an eye out

But there was no target is just the pokemon disobeying orders regardless of the type of move or type of pokemon. Case in point, my Baaschaf (dark/fighting type), I had it use stomp (normal type) on a Magikarp (water type) and it responded "Baaschaf ignored orders, Baaschaf used stomp, but there was no target..." This was only due to it being level 33 before I had beat the 3rd gym, but it's just part of them disobeying orders.