Update:

I read the suggestions posted in "New messages do not appear" on the mozillaZine webpage. I changed my Thunderbird setting to download messages automatically. (Previously, I downloaded them manually,) Rebooted Thunderbird. This time 8 of the earliest posts downloaded, then stopped. I tried again to manually download the remainder. Again failed. The following error messages were reported:

Could not read chrome manifest 'file:///C:/Program%20Files%20(x86)/Mozilla%20Thunderbird/chrome.manifest'.

Timestamp: 4/16/2015 4:16:34 PM Warning: mutating the Prototype of an object will cause your code to run very slowly; instead create the object with the correct initial Prototype value using Object.create Source File: resource://gre/components/steelApplication.js Line: 783

Dave

try disabling anti virus scanning of your mail. Most connection that start well and die are because the anti virus is messing up

Thanks Matt for your suggestion.

Several days ago, I had over 1,600 emails in my Inbox. I compacted the folder, then removed all but 5, compacted again as suggested on a mozillazine.org web page. This seemed to help. But the problem continues.

Deactivating Kaspersky Anti-virus sometimes seems to work, and sometimes doesn't. So far, I've been able to download my email in small batches, and after several tries I'm able to download all currently available emails. I switched back to manual email downloading rather than automatic when Thunderbird boots up.

I'm getting a lot of different error messages, some of them probably not relevant to this issue. A few of them refer to Javascript issues.

Another error message that pops up occasionally, but not always, is this one: Could not read chrome manifest 'file:///C:/Program%20Files%20(x86)/Mozilla%20Thunderbird/chrome.manifest'

Dave