Instiki users - Jul 2006 - [Instiki] Instiki not showing initial compose page on Windows XP

When I load http://localhost:2500 in Firefox, it loads a blank page. As
you can see from the counsel log below, the page request is generating a
500 error.  Any idea what might be causing this?

Thanks very much, in advance, for any help!
Simon

C:\ruby\instiki-0.11.0>ruby instiki
=> Instiki started on http://0.0.0.0:2500
=> Ctrl-C to shutdown; call with --help for options
[2006-07-05 09:51:44] INFO  WEBrick 1.3.1
[2006-07-05 09:51:44] INFO  ruby 1.8.4 (2005-12-24) [i386-mswin32]
[2006-07-05 09:51:44] INFO  WEBrick::HTTPServer#start: pid=4084 port=2500
127.0.0.1 - - [05/Jul/2006:09:51:51 Central Standard Time] "GET /
HTTP/1.1" 500
0
- -> /
127.0.0.1 - - [05/Jul/2006:09:54:09 Central Standard Time] "GET /test
HTTP/1.1"
500 0
- -> /test
127.0.0.1 - - [05/Jul/2006:09:54:30 Central Standard Time] "GET /
HTTP/1.1" 500
0
- -> /



Specs: just installed latest ruby and latest instiki
OS: Windows XP w/ SP2