Thanks Peter and Jamie for your suggestions.
I didn't have any white space, and I didn't have ?> closing tag. I actually read the tutorial before :-)
I was scratching my head all day today, and finally I found the cause. Out of habit, I had UTF-8 declaration on the file header, EF BB BF. I didn't realize this until I opened the file wit Hex Editor. Apparently Drupal didn't like this. Now I know better.
Thank you!
-- - Hiro
Hiroaki Honshuku, A-NO-NE Music, Greater Boston http://a-no-ne.com http://anonemusic.com