Unfortunately, Sudoku has stopped. Why?

I read Hello Android book and I wrote a part of a Sudoku program but when I click on the New Game button and I select one of options and I want to write a number in the tile, the program stops and shows this message:

“Unfortunately, Sudoku has stopped.”

Why am I getting this error? How do I solve this?

I dot know which part of the program has problem because of this, I’ve uploaded the program, please download this and see what’s the problem?

http://www.4shared.com/zip/tMoGFKSR/Sudoku.html?

Ya i know “Fahimeh” because i have faced the same issue with sudoku. But now, everything is fine.