Can't catch pokemon - Charmender

[Pile04]

I was farming Charmender for the Mega quest, and when i finally found charmender twice, and in both times it says i can't catch more pokemon, but i had space on the team and on the pc. After the first one I try to catch a Rattata and I had no problem at all. When i found the second charmender, it happened again. Its a tier 8 pokemon, its hard to find a good one. Its not fair that something like that happen.

[Silverage]

You are limited to 900pokes in total, there are more space in pc but you can't catch a pokemon if you have 900, that's probably the reason