[Konstantinos]

You open the file with mode io_read. You count the lines and you try to write. You need first to close the file and open it with mode io_append or io_write (removes everything and writes from the first line) so you can write to a file.

But still, you never used count so what is the point of counting the lines?

EDIT: I read your thread here: https://sampforum.blast.hk/showthread.php?tid=511564

Do you want to just write to the last line that's why you wanted to count the lines? That can be done by opening the file with mode io_append.