Application working with CGI but not with FastCGI

I have started rails some week ago. I have deployed my application to
production sever which is a shared host with FastCGI enabled. This
application is actually Radiant CMS and working fine if I am using
dispatch.cgi. But whenever I use dispatch.fcgi the browser takes a lot
of time and finally it stoped with blank screen - no error. I have
created a simple test application but the same problem is coming with
it also.

Then I have run the dispatch.cgi and dispatch.fcgi on command line and
following output is coming.

[~]# ruby radiant-0.6.1/public/dispatch.cgi
Status: 400 Bad Request

[~]# ruby radiant-0.6.1/public/dispatch.fcgi

So it seems that dispatch.cgi is returning some output but
dispatch.fcgi does not given anything not even a error.

I have searched over google but could not find help.
Kindly help me for sorting this out.

Deependra S.

Is there nobody to answer ?