Hello everyone,
I think I can put this one to rest. The culprit, you ask? Skype.
The web server was always being tested (on multiple machines, no less) after Skype had been started. Quit out of Skype, then restart the web server, and tests should go through just fine.
I suspect, though, that it's not necessarily Skype causing this problem in all cases. My theory, and please correct me if I'm wrong, is that Skype runs as a web service on standard web ports (80/443), listening for the Skype service to send it messages. This is based on the idea that only one service can attach to the a specified port at any given time. All subsequent services simply do not attach.
Once I turned Skype off, I was able to access my web server again. And just as a sanity check, I turned Skype back on ... sure enough, my web server failed to serve. Now, if only I could understand why running my web server on a virtual machine (which does not have Skype running also failed, things would be peachy.
Hope this helps some other frustrated soul!
Regards,
Flint
P.S. I actually stumbled upon the solution by changing the port number my web server was working on ... since pretty much all of the NetTalk examples use ports other than standard 80/443 ports, and they were working fine. I normalized my web server to conform to the examples as best I could ... voila. Then I tried to understand the common denominator on each of our three failing test machines (which was not a variable on a fourth machine on which the web server operated just fine). Enter Skype.