How to fix "ERR_SSL_PROTOCOL_ERROR"?

[dana_dany]

Hello. My supervisor has a problem with the Dropbox web page, so she cannot even register on her computer.
When she accesses "www.dropbox.com," she gets the error message "this site can't provide a secure connection (ERR_SSL_PROTOCOL_ERROR)."
It happens both in Chrome and Microsoft Edge. Also, she can access to other sites except for Dropbox.

So, I did several works, but it still has the error message. Please help me.
1. System data and time check -> it is right
2. Removed all the Internet usage history from the browser
3. Removed SSL condition from Internet option
4. Disabled Experimental QUIC protocol and TLS 1.3 in Chrome
5. Deactivated the vaccination program
6. Lowered the firewall
7. Disabled all the extension programs in the browser
8. Set the Internet security level to medium
9. Flushed all the DNS from the cmd

I have no idea what I should do next.

[Walter]

Hey there @dana_dany - sorry to hear about this.

Could you have your supervisor clear their browser's cache or try another browser, preferably with no extensions or plugins running and let us know how it goes?

If they have an antivirus, firewall and/or VPN/proxy setting running on the affected computer, they can temporarily disable them too.

If they still get the same error, please send us a screenshot of the exact error so that we can have a visual as well.

Thanks!