Yes, I have tested without SEF, and that is the one that is working...
Here is what I've done:
1. Checked to make sure the files are actually there.
2. Removed and reattached the files.
3. Deleted and uploaded new files.
4. Checked File Permissions.
5. Created new items to link files to.
6. Created a new "File" field.
7. Turning of SEF.
8. Turning off SEF just for the download.
9. Changing from button link to file link and back.
The problem is that ALL files right now are being given "/download?fid=55&id=515" ALL with the same id, which apparently does not exist, instead of "/download-dp83?fid=55&id=481" with a correct id.
ALL of the items entered before 1/18 work (and continue to work, through all of the tests). None of them since do. FLEXIcontent has stopped connecting to the correct files, somehow.
Last item download that works:
www.365daysofsewing.com/sewing-l
... ics-cotton