Was it a copy of a copy of a copy? (or any variation)
I have run into that before.
Each copy introduces a bit of error (not an exact copy)
and successive copies add more error until finally
a copy is so far off it doesn't work.
It's not enough of an error that you can see it,
but it is just enough to keep the key from not working.

Pooh Bear

I see...... thank you.... I guess that it is a copy of a copy.....

Take your key to a real locksmith shop. They will measure the key to determine the code, then they will cut a new key using a Code cutting machine. That will produce an exact factory new quality key. Usually they will do that for about the same price as having a key duplicated in a hardware.