Red triangle, won't access one account

Yesterday I was on emClient v.9, the latest version, everything was working OK until without changing anything, one of my email accounts ([email protected]) got the red triangle, Connection Failed, but another account (pndtennis.org.uk) which is set up exactly the same way, carried on working OK. I have checked through my server, and the emails are working OK there. Turning emClient off and restarting, and rebooting Windows makes no difference, so I know the problem is with emClient. So I decided to upgrade to v.10, but the same situation still applies - I have the Personal Pro licence for 3 users. I have a laptop with an old version 9.2.1222 and that is receiving the emails from the problem account OK.

Here is a screenshot of my current v.10 display

You can see the 2 identical accounts that I’ve mentioned on the screenshot. I think I’ve checked everything I can, but I still have the problem, unusual on emClient that I’ve used for years.

Help, please!

Just now, emClient crashed with an error (I submitted the report, something about 99 errors), then when it reloaded the red triangle problem has gone away!

Haven’t a clue why, happy as I am it’s gone away. What do you think happened?