I found this here at elk.net, I was pretty sure it was fixed a while ago, but I may be wrong so I'm reporting it again in case someone remembers better. O:-)
Type of error: Undefined
8: Undefined index: letter_links
http://www.elkarte.net/community/index.php?action=memberlist;sa=search
/.../themes/default/Memberlist.template.php
Line: 72
We did fix it ... partially :P I've seen this show up from time to time and think it happens when a search returns no results.
Ohhh!
That makes sense, I was wondering when the heck was going to appear. Thanks for the debug!
Fixed #2405