header problem

[MarYJ]

header("Content-length: $size"); // tells browser how large the file is

ok, i have this problem, whenever i run this script it throws me this warning

Warning: Cannot modify header information - headers already sent by (output started at /vol/project/2004/V362/g04v36203/admin/jj/includes/navigation.inc:222) in /vol/project/2004/V362/g04v36203/admin/jj/parts/download.php on line 29

The way i understand it, it is because i already use header for something else....
I do need to go this way for downloading a file, don't i??

Is there any other way to overcome the header problem???

[exutable]

I would try to use window.location='<? echo "$something"; ?>';

[jpr]

Have you already put out some other form of output besides a header? Like an echo or print statement?