If the dataset is a collection:
Downloading dataset collections is producing this error at Galaxy Main https://usegalaxy.org right now. Tracking ticket with details: https://github.com/galaxyproject/usegalaxy-playbook/issues/85.
My guess is that is what is going on, but please confirm. And if you are working somewhere else, it would be interesting to know where. I'm not 100% certain yet that this problem is server-specific.
If the dataset is a single dataset:
Please double check your usage and try both curl and wget. One of these should work for everyone -- but both will not work for everyone. Full options: https://galaxyproject.org/support/download-data/#download-tip-big-data
$ curl -o outfile --insecure '<link>' # ignore SSL certificate warnings
$ wget -O --no-check-certificate '<link>' # ignore SSL certificate warnings
Please let us know if single dataset download is a problem you cannot resolve. We'll want to follow up on where you are working, what the datatype of the dataset is, confirm your command-line syntax, etc. to test and see if there is another server download issue going on.
Thanks! Jen, Galaxy team