Sorry I missed the version number. Since it was working fine before, has your browser/browser version changed? What browser + version are you using right now?
For 1.8.2 we were using an older version of plupload which had a few problems with uploading files.
Finally, if you need to resolve this issue really fast, I would suggest uploading the files manually to the server via ftp or ssh/scp, and then using the airtime-import command.