Is mainly a technical fault. Please wait for sometime and try to open it by tommrrow.

If you can't add attachments to Gmail messages then you need to add an allow exception to allow pop-ups for this Google website (mail.google.com). Easiest to do this is to click the padlock on the location bar and click the "More Information" button to open the "Tools > Page Info" window with the Security tab selected. Proceed to the Permissions tab Remove the tick on "Open Pop-up Windows" > "Use Default" and click the Allow radio button to change the permission to allow pop-ups for the mail.google.com domain. Google is looking into this issue, see: * https://productforums.google.com/forum/#!topic/gmail/q0BxcGOa6pk