Same here. Error 2038 when trying to upload a 350Mb zip file. Always bombs out about 2/3 of the way through the upload. Running Firefox 14.0.1. I have NoScript plugin installed, but have allowed all scripts on your site.
This may also have something to do with the flash plugin as the uploaded is flash based. I would suggest trying a diff browser and/or re-installing flash if you're getting this error consistently and not uploading a file that's bigger than 1GB.