The reasons may vary, typically you need to check:
- your firewall or antivirus, if they block the connection
- make sure the server you broadcast to is actually available, for instance, you can try opening server admin page from web browser - if it doesn't open, then the server is definitely unreachable
- check that the server you broadcast to doesn't block your IP
You should contact your stream host about the issues. If the settings are correct (correct server address, port) then there's nothing else you can do from RadioBOSS to make it work.