Impossible to do a chain ( pokeRadar)

[Iron]

The most common mistake is not choosing a tile of grass that's 4 tiles radius away. Not just four steps, mind you, but a radius of four - could be four steps east and four steps north, for example.

Another thing people don't know is that you can re-try the PokeRadar if you don't get a good patch of grass. Simply walk another 40 steps without leaving the patch of grass or stepping into any shaking tiles, then use the Radar again. Your chain continues.

But all this is in the thread Mikaruge linked.