Learn more about this change here.
For help regarding Aternos, we recommend you to visit our support center.
Maybe the world is corrupted? Did you check the server console yet?
What size is the file? It might be too big.
The server console is only shown when the server is online. Can you tell me your Aternos username?
We only offer mod packs in their default configuration, Vein Miner is not included in it.
I just checked your server. Your world version is not compatible with the mod pack version you use on your server, that's why the server does not start.
Aw that's sad. Veinminer makes it more easy and less laggier. 
What is the version of Sky Factory that the server offers? 
It's 2.4, but you could have looked it up on your own too, it's shown at the My Server page…
