problem using header

[danman]

I must have tried a lot of different downlaoder scripts, and they all keep saying this:

Warning: Cannot modify header information - headers already sent by (output started at /var/www/dl.php:44) in /var/www/dl.php on line 59

its driving me mad. Is there something missing on my server?


---Edit----


Ok got that fixed, but my zip file just appears as html/ascii junk on the screen. any ideas what can cause this?
the line is basically: header("Location: $url/$file");