Access to uploaded image files denied

I am unable to view my original uploaded files, though the presets are working fine. I am using Organic Groups for access control and am using Private file transfers.

If my uploaded image is to an OG group, then when I try to view the original file I get a Access Denied error (403) for the image. If the upload is not to a group or the group is public, then the original image downloads fine.

The reason that I believe this is an imagecache issue and not an OG issue is that I don't get the same behavior with uploaded (non-image) files. They are saved in the same directory as my uploaded images, and they can only be downloaded if the access is granted, but I never get an access denied error. I am using filefield and imagefield for managing the files and images. As a further test, I created a content type that allows me to upload a file and an image to one node. I am then able to download the file but not the original uploaded image. The only difference in the two files (non-image and image) is the existence of imagecache inbetween. BTW, the imagecache presets are all working fine.

Using Drupal for Firebug, it appears that when I get the access denied error that for that page Drupal thinks I am now User 0 rather than whatever user I'm logged in as (including User 1).

Drupal 6.12
Imagecache 6.x-2.0-beta9
OG 6.x-1.3
Filefield and Imagefield 6.x-3.0
Private file transfers, directory outside

Any ideas? I'm not sure if this is a bug, a conflict or a configuration problem. Or is there something other than imagecache in the pipeline that might be the problem?

Thanks