[konidias]

This has happened to me many times also.. a way I have found to prevent your level from getting erased is this:

If you hit play and the level shows up blank (or the level shows up blank at any time) close the Graal exe immediately and open a new one, then open the level.. usually the level is still in tact.. its when you go back into the editor from playing the empty level or whatever that it ruins it permanently..

I had this problem yesterday and I just closed and opened graal, and the levels were still there... so don't do anything but close graal after the level goes blank/full of the same tile