SCGI on Apache 2 send_file Error

Hi,
My program send s PDF file to the browser using send_file.
Everything
works fine in Webrick but when I switch to SCGI/Apache, the PDF file
just
does not get streamed to the browser. I checked the error logs and this
is
what I got from server.log

Mon Aug 14 12:51:24 2006] [error] [client 127.0.0.1] malformed header
from
script. Bad header=%PDF-1.3: 26, referer:
http://localhost/qual_reports/generate_final_release_report
[Mon Aug 14 12:51:24 2006] [error] [client 127.0.0.1] (500)Unknown
error:
scgi: Unknown error: error reading response headers, referer:
http://localhost/qual_reports/generate_final_release_report

I have no idea why this should be happening and the scgi.log does not
show
any error either!

Any help will be highly appreciated.