make the the grid 25x25 and the cell size 25 from yousr pathfinding sprite and use the sprite solid between 25 size..
I have tried this with 32x32 but it hasn't worked so far
Edit:aslo what do you mean by make the grid 25x25 I don't see a grid plugin
You could try this plugin:
It probably can be used to do what you want.
Or you could implement pathfinding in just events. Here's my latest attempt using a hex grid. It actually should work if you change the hexagons to squares and position them on a grid. You just need to tweak the collision polygon into a square with beveled corners so diagonal cells won't be used.
I have looked into the astar plugin but I don't understand how it works