You didn't provide much information. Windows version?
I've seen the error before at these forums but cannot recall the answer. But the same answer does not always apply anyway.
I can suggest these things:
http://www.gnutellaforums.com/333278-post2.html 
However if you need the LW 4.18 installer, get it from the Older Versions link at LW's download page.
Delete the LW preferences folder before you install, if you had LW previously. Found here
Deleting LW prefs folder or for vista see
http://www.gnutellaforums.com/genera...der-vista.html & delete the entire LW folder.