I have to say that lighttpd is the most annoying piece of software. Every time piaware updates the config breaks for one reason or another and I have to rummage around to find out what has broken. In this case there was a duplicated server.modules += ( "mod_setenv" ) and a duplicated \data section that was preventing it start. It’s probably OK if there is only one thing using it, but if you have any other software installed it then it’s highly likely to be problematic.
Edit - just noticed the other thread talking about this issue if people look have the problem and look here first.