Thank you for the replies... I definitely don't relish trying to downgrade, but I couldn't figure out what else to do. The issue is as follows:
I have custom modules in my Portal... If I access the Settings of the module while logged in as host, it works fine.
When I added my own custom Settings control in the module definitions and then access the module settings, nothing renders inside the Content Pane at all. Even if the custom settings control has no code in it whatsoever.
I at first thought this was a server issue since my local versions work fine, but I realize that my dev version is 4.9.2 and the installed server version is 4.9.3. I downloaded the application from the server to my local machine and attempted to load the Settings of a Module that is customized, and I get the same results: nothing renders inside the ContentPane at all.
I have also tried this with different skins, including the default - this does not seem to be the problem.
If anyone has any other ideas, I am MORE than happy to try... Like everyone, I just need it to work. :-/
Thanks again for the replies - much appreciated. I will fight with it again for one more day and then try downgrading tomorrow if it still does not work.
(If it matters, I am using MS SQL as the database - there is no dev DB; both installations point to the exact same tables)