Users of GMail cannot upload attachments.
SecureSchool, ISBossBox, LibraryDoor.
GMail made changes to their services recently that have caused intermittent issues with certain computers that try to attach files to their e-mails from their GMail account. To fix, just login to your GMail account and click on Settings > Under the General Tab scroll to the bottom and select the option: Always use https (under the Browser Connection option) > Click on Save Changes. Log out then log back into your account and you should be able to attach a file to your message.