I have found additional information. From the account without administrative privileges I launched Thunderbird in Administrator mode. I then created an e-mail account (which exists on my provider) and it works. I can download messages. I then closed Thunderbird and re-started it without administrative privileges and when I click on get messages the error message shows up.

if I switch to a different account (which is not an administrator) I have two e-mail accounts ...

... Now if instead I launch Thunderbird as an administrator, I only see one e-mail account (which is the one set up under the administrator account)

You created two different Thunderbird profiles, one underneath the Administrator Windows account, and one underneath the unprivileged Windows account.

I get the following error message: This site attempting to identify itself with invalid information. If I click on get certificate it says unable to obtain information from this site.

Please post a screenshot with the error message. https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

Here is a screenshot of the error message I get

If I click on get certificate it says unable to obtain information from this site.

You're trying to access port 143 on the server. That's usually used for plain text IMAP access. IMAP TLS would use port 993. Are your server settings correct?

Something funny is going on here. I got it working and here is what I did. First under window settings I had three installations of Thunderbird (different versions). I uninstalled all of them down loaded the latest version and installed it. I tried to create an account inputting name, e-mail address and password. I then clicked on configure manually imap and smtp ports were set to auto. Clicked on test and imap port was changed to 143. No error reported I then clicked on done and got an error message unable to communicate with server. I changed the imap port to 993 clicked done same problem. What I had to click on cancel. Create an account again but this time instead of clicking on configure manually I clicked on continue. It downloads data from my provider then I have to go to configure manually to enter a proper user name, change the port to 993 click on done and it works. What is really peculiar is if I log in with an account which is not an administrator create the account using the above procedure it works fine. Getting server properties it shows imap port as 993 but if I log in with my administrator account and do the same thing it shows imap port as 143 and I have no problems also when I thunderbird downloads data from my provider it sets imap port to 143

if I log in with my administrator account and do the same thing it shows imap port as 143 and I have no problems

It is a bad idea to run Thunderbird with Administrator permissions. I'd suggest to delete the profile you created as Administrator. Since your account is IMAP it shouldn't matter, you'd see the same messages in both profiles.

Why you can access port 143 in one profile but not the other, I don't know. It's probably something you'd need to clarify with your email provider what the correct server settings are.

Thanks christ1 for your help. I contacted my provider and port 143 is correct but I can also use port 993 maybe this is something the developers can look into regarding the workaround I had to do to create the account

Server settings are different for using different ports, and hence for your two profiles.

With port 993 'Connection security' should be set to 'SSL/TLS'.

In case of port 143 I'd expect 'Connection security' to be set to 'None'. I.e. everything, including your password, will be transmitted to the email provider's server in the clear. This is bad, and shouldn't be used anymore. My best guess is you had it set 'SSL/TLS' as well, hence the error.

On the account set to port #143 security setting was set to starttls. I have changed the port # to 993 and the security setting to ssl/tls.