About a year ago, I created a custom button on Leads for Convert with a purpose of having 'Do not create a new opportunity upon conversion' checked by default instead of unchecked.  As of a few days ago, it no longer works and I'm receiving the URL No Longer Exists message.  I've included the script below.  Your help would be greatly appreciated in resolving this.

"/lead/leadconvert.jsp?retURL=%2F{!Lead.Id}&id={!Lead.Id}&nooppti=1"