It was indeed the problem with the 4:3 encoded 640x480 file.
I re-encoded it to 16:9 in 1280x720p , uploaded it to Youtube to make it smaller and then downloaded the 720p File from Youtube , which was then only about 500 MBytes big and uploaded it here on DLive and then it finally worked... Costed me a whole day to figure it out inclusive the
way to make a good animated GIF thumbnail unter 1 Mbytes from it...