It'll be hard to find a solution to the issue because of the "Unknown Error", the issue isn't specified.
See if you can find the cause by enabling logging by ticking "Tools->Preferences->Misc->Write logs to file", restart Electrum.
Reproduce the error in the next session while Electrum is logging, then check the recent "electrum_log" in "logs" folder inside Electrum's data directory (location).

But AFAIK, it's the replacement error message if the server is trying to send you a malicious phishing message.
If you're using an old version, update it ASAP.

It's not similar.
That's only the generic error message that appears when there's an issue, the actual issue in the one below it.
In OP's case, "Unknown Error"; that link's issue was "insufficient fee".