All the most common third party vpn providers give users two files

• One like somename.ovpn and another like xxxx.crt
• somename.ovpn has reference to xxxx.crt

1. open somename.ovpn in notepad

2. replace whole line : "ca xxxx.crt"

with

"ca [inline]"

yes exactly ca [inline] with square brackets without ""

3. at the end in somename.ovpn opened in notepad already,

add txt content of the file xxxx.crt (open in notepad in septate window)

like 

<ca>

text copied from xxxx.crt

</ca>

4. save somename.ovpn in a location like d:\aa\bb\somename.ovpn

5. in the screenshot by original poster of this question, click on browse, select d:\aa\bb\somename.ovpn

6. give valid description

7. username and password is must as per the party who sent you somename.ovpn

8. Wait for status to change to "connected" from "connecting"

@_hhh_ Please note that I use a consolidated OVPN file which has the CA tags embedded. Attaching a snapshot of the OVPN file content for your quick reference. As in the OP, the same OVPN file works flawlessly in the "OpenVPN for Windows" client.

Also attached is another attempt to re-upload the OPVN config file, which met with the same failure!