When I upload file attachment larger than ~1mb to Gmail using the Chrome web browser (v18.0.1025.33-r122015 google-chrome-beta on Ubuntu 11.10), the uploading will always fail after a while and Gmail will retry, resulting in an infinite loop to attach the same file.
Workaround: Use Firefox to attach such larger file attachments in Gmail. It works for me on the first try with Firefox 10.0.2.