Are you uploading using HTTPS based connection? See:
(this is about Flash runtime though)
Interestingly there is no exact wording on Air runtime support for file size uploads but there is for Flash runtime:
Although Flash Player has no restriction on the size of files you can upload or download, the player officially supports uploads or downloads of up to 100 MB.
> above could be related to your comment about single small request being dispatched before main upload.
> Because you're using (used) at least two uploads you could go and see that thread as well:
Peter, my issue is similar to what is being discussed here, http://forums.adobe.com/thread/796003, but not exactly the same. When my first upload completes, it actually forces the user to wait about 5 seconds before the next upload of the full 120MB file commences. Plus, this is still only occurring on Linux OS's.
Also, for the record, I am not using FileReferenceList to upload but rather the File API using the upload() method. Very straight forward. The URLRequest object points to a simple ruby cgi script and the contentType property of the URLRequest object is 'multipart/form-data'. We aren't doing anything fancy to this POST since the ruby script handles all the heavy lifting.