What size is your tilesheet?what are you trying to do (create map, edit sprites, something else) ?
Width 140
height 492
I generated it from the "set as atlas" feature, And I'm trying to use it to edit maps
Images generated with "set as atlas" are not supposed to be reused directly.
What you could do is edit the tilesheet in another image edition program, and maybe split it into several tilesheets.
You can also change the size of tiles from Project > Settings
