Forum search has not been working reliably since like 2009 (or was it 2010?).
You can try the topic name filter:
http://peachyforum.com/filter.aspx?ForumID=11&q=mary-lane
There is a trick here. With multiple search terms, you need to put - between them, otherwise there will be no results:
http://peachyforum.com/filter.aspx?ForumID=11&q=mary+lane
Alternatively, you can search the forum with Google:
https://www.google.com/search?q=mary+lane+site:peachyforum.com