Could be either you've tried to change the default lfslapper.lpr script, and made a mistake somewhere, or the script has become corrupt in some way.
Assuming you haven't changed the lapper file in any way, the easiest way to solve it would be to just install it again.
If you have changed your lapper script, backup the file(s) you've changed, install brand new version, then start making small changes to the new script and test it everytime you change it.
Or it could be that in your swear.txt file or in the lfslapper.lpr file (under $SwearWordsList) is a word that starts with an exclamation mark (!), and lapper doesn't know how to deal with it.