how do you get pokemon to eat more berries when they wont in pokemon platinum

[Footprint]

how do you get pokemon to eat more berries when they wont on pokemon platinum?

[Zidarose]

Pokemon will only really refuse to eat berries when they no longer will have an effect on them. This could mean full HP, PP or the stat is already at its minimum.

If you have been feeding a Pokemon Poffins, the treats made from the berries, they are full. This is shown in their Sheen gauge. Once this is full however, it is permanent.