Code sometimes does not store .vtu file

Hi All,
I am trying to store .vtu file in my code. However there is a peculiar problem. It sometimes store vtu file sometimes not. Is there any reason?

I think you have under windows and you do not kwon where is the file in directory tree
so first seach the file or put the full path name to write you Stu file.

Dear Professor,
The file is stored sometimes in the directory sometimes not for example when I restart the computer it stores but after I compile one program on freefem, it does not store the vtu file.