Did you shake well before using? Could be that it's separated a bit, or the alcohol could have evaporated out of it too much. Do you still have a seal inside the lid? I know mine falls out every once it a while. If it doesn't get a good seal, it could have dried out or evaporated some.
Try shaking it up real well, and if that doesn't work, add a little bit of denatured alcohol into it and shake it up again.