It might mean that the KB of your file is too big. I don't really know the limits of KB on this site but there might be a limitation.
sorry if im dumb but what's kb? ;-;
Basically KB stands for kilobyte, what that means is the larger a gif or file is, the more kilobytes it has. If it's really big, it could have MB or GB (megabytes and gigabytes). If a gif only has like let's say 10 frames, the KB size will be small. If it's over 100 or 200, it'll be huuuge and probably would end up being a megabyte.
oh okay! is there still a way to make that gif my icon? i just think it's really cute and agh
http://www.auplod.com/u/puoadl6e4bf.gif