Mov and mp4 files on Adobe Express

Hi, I'm trying to upload an animate file (that is an animated web banner) onto my adobe express presentation. I've downloaded as a mov at first, but when I try to upload it says: "Sorry, we were unable to upload animatewebbanner.mov to your project." Then I converted it to an mp4 which uploaded fine, but then it only plays the first 3 or so seconds and won't play all the way through. The same thing happens when I download as a gif (it uploads fine but will only play the first couple seconds.) 

How can I upload this animate file correctly??? I have quicktime installed, so not sure why it's working.