BTW I am using fastcgi so I changes the dispatch .cgi to dispatch.fcgi in .htaccess. I see another one in vendor/.../apache.conf and changed that too. Now I get a real 500 error page that says the same thing.
I can run test apps on either WEBrick or Apache but Instiki runs only on WEBrick. With Apache I get the 500 error "%lt;h2>Application error%lt/h2>Rails application failed to start properly."