Hello, Wilson;
Thank you for your insight and the knowledge that this error message could be reporting an issue with being logged in. Armed with this information, I decided to run a few more experiments before trying a fresh install on another machine (though, I expect that would have worked fine given what I have learned).
Though I didn't expect any problems, I decided to look at File -> Master Login. No problems there, but I decided to try re-entering User Name and Password. No change in download behavior from this.
Along the same line of thought, I selected a few representative groups (some which were updating properly and others which were not), then 'right click' -> Group Settings -> Group Logon tab and checked that Yahoo User was either (default) or my Yahoo User name, and re-entered the Password. I tried several combinations of not "messing" with the Password or Yahoo User, entering new ones, changing one but not the other, etc. Again, no change in download behavior no matter what I did here.
Before I explain my next experiment it's important to know that I've been using / testing PG Offline for quite some time now, including during the period when the "Object Reference not set to an instance of an object." message was very common. This was during the time when Yahoo and/or PG Offline was changing the way that "authorization" was working.
What is important here is that at some point during those days, you recommended that File -> Options -> Workflow tab -> Skip authorization be selected. Long ago, I successfully ran with "Skip authorization" selected for several versions and over a period of weeks to months. I don't remember ever specifically clearing that selection, though at some point it may have been deprecated anyway and things just started working without it...
I decided to try selecting it again. Now here is where it gets interesting! I expect there may have been a "stuck" value in a preferences file or registry key. As soon as I selected "Skip authorization" and exited the tab clicking "OK", download behavior changed!
The download activity during either Refresh or Start (with a group selected) appears to now be working correctly! For the first time in a long time, I now see the messages
<timestamp> [group name] Logging in with account
<my Yahoo Login name>
for each group and the group messages are now being downloaded again!
When I later looked back at the File -> Options -> Workflow tab -> Skip authorization, it appeared unselected (and remains so). This is why I suspect that there was a "stuck" or corrupted field for that value, causing PG Offline to skip logging in before each group synchronization. It is still mysterious that some groups would synchronize without logging in, AND that the groups which would work and those that wouldn't changed and appeared somewhat random over time.
So, for now, all is well. I've exited and restarted PG Offline many times and the behavior now seems consistent. ALL of my groups are now synchronized, which hasn't been the case for a long time. If you have some users who are experiencing a problem like this, it may be worthwhile considering that a preference value may be "stuck" or corrupt.
So, I won't take any more bandwidth. As always, thank you for your help and insight! I'm back catching up on some groups which I haven't been following for months. And, enjoying PG Offline, of course...
Best Regards,
Dave
Erie, CO