If you're on linux, and you're root, type

mount -o remount,rw /path/to/mount/point
[download]

Where /path/to/mount/point is the path to the mount point under which CGI tries to write its temporary files. Read man mount for more informations on mount.

And please never type example code (especially not as root) unless you understand what it does - it might do serious damage if you do.