.flv files not uploading

When I try these files, I get the message "The image upload failed" and "the Video file field is required" - the same when I click upload and save. Here's what I've got:

Drupal 6.3
php 5.2.2
mimedetect
cck (with a custom content type for flash videos and a file field named "video" for those videos as well)

I am not running image.module, as the error message might suggest. Can't I use filefield to upload these files? I get no errors when I try .swf files.

Thanks for your help!