Has the old site the same package versions as the new site?
Was "/image/?m=download" really the exact url?
Can it be that you ran out of disk space when copying the content-repository-files?
In general, there is not much magic about xowiki::File objects. Check out, whether the files exist and have a sensible size in the fs.
select i.item_id, i.name, content, content_length from cr_items i, cr_revisions r where content_type = '::xowiki::File' and r.revision_id = i.live_revision;
Btw, the actual version of xowiki in CVS head supports import and export of xowiki instances including files (these are encoded as base64 in the serialized representation). You might check, whether this solves your problem without looking into the details.
