I went to catch Kyurem, and my party was full. I used a Masterball as soon as i encountered it (level 50 one) , it said "kyurem escape , your box is full" something like that. i dont know what the problem was , i even threw my ultra balls but same thing prompted , even my master ball got consumed.

Can i know what the issue is? or can you explain what should i do now? because im really stuck now.

It means you had 900 pokemon in your Box (you can check it in the Total Pokemon in your trainer card id ingame) and you thus couldn't capture any more pokemon, as you're in the limit :/

 

I hope Staff can help you with it... I'm sorry :(