I don't know whether to call it error or what from Google in their new mobile Gmail interface. We noticed that when composing a new mail with our mobile device on the new mobile Gmail interface, and when trying to attach file to the message, we could barely see provision for that, in fact there is no provision for that. so that is one of the downside of the new mobile Gmail interface, because in the former version you can easily attach file when composing a new mail. But trust Naija, there is always a way out whenever this type of issue arises. The solution to that is for you to switch from your mobile version to your desktop version, with that you will be able to attach your files to your composed messages with your mobile device.
http://highteknology..com/2013/09/how-to-send-mail-with-attachment-on-new.html

i'm also experiencing the same problem i do hope gmail does something to correct that error..fast