In our university there is a very low connection speed limit but there is almost no limit on number of connections.
I had no problem with aria2c 1.9 but since 1.10 I get "max-connection-per-server must be between 1 and 16" message after:
aria2c -k1M -s50 -x50 "http://just-one-url"
It would be great to reconsider max-connection-per-server limit.