I think it is just too huge. GIF, 2814×1876. If it has more picture to it I can't tell because it takes a while to load.It could be possible you didn't upload all of it, but it really needs to be smaller if it is going to be animated to fit the screen. More like 700x500 at the most. This is about that size and the file size is 1.6M [link]
First, if it is an animation how is it just one frame? Second, I have uploaded things with over a hundred frames, so unless you try to use it for your icon, file size doesn't matter. How big is the file(pixels)? If it is bigger than 150 by 150 pixels, then you need a preview picture. This is a picture you submit(that DOESN"T move) that people will see unless they click on the picture. Usually they say click to preview so people know its an animation and it is similar to what their pic is of. When you click submit, it should show a red bar at the top saying what you need to do. If it says something about needing a preview image, upload one. Otherwise, if your gif isn't actually an animation(doesn't move, sorry if i sound condescending) then I suggest saving it as a png and uploading it, they are easier to deal with. Other than that I don't know what to tell you.
Umm. What is your preview image file type? (Just in case you don't know, the file type is what comes after the .) If it is xcf, bmp, gif, or something like that,deviant art can't handle it. Do not fear!! Just open your preview image in whatever(PS, gimp, or from your picture file, whatever you used to work on it) And click save as. The name of your preview image should show up, so, for example, it could be iamperfect.gif or something. All you do is go behind the . and change it to iamperfect.png Then just make sure you upload the png file to deviant art, not the xcf, gif, whatever(thats for preview. DO upload the gif for your animation, if you want it to move).