are you using a *nix system?
Can you please try opening a terminal and using curl to getinfo via RPC?
curl --user <same as in nu.conf> --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "getinfo", "params": [] }' -H 'content-type: text/plain;' http://127.0.0.1:9091/
after changing the username as in nu.conf and sending the command you will be prompted for the password.
Can you paste the output ( redact the ip address please ) ?