Error on cancel

Hello!
I use CommonDialog to open (text)files to a RichTextBox, and saving them again in my app.
It all works well, but if I press Cancel, the program dies. It's not the CancelError property, it's set to off (and it's not that error), so I don't know what to do.
Also, if I have opened one file, saves it, then makes a new file and takes Save As, and presses Cancel, it returns to the previously opened file.
What shall I do?

Pentax

Post some code .

Well, it worked out.
The problem was, without a filename, a Do-While-loop wouldn't end, so it just wnet on, and on, and on...