Unknown Error from Internal Server Posting - Worked Fine a Month Ago

I use Captivate to create CBT (Computer-Based Training) applications that are called from our web application. I have had our internal server posting using ASP/C# working fine for the past 2 years and just recently (somewhere over the last month) I am now receiving an "Unknown Error" in the Status message during quiz result posting. When it was working, I was parsing the Filedata (output) from the posting to extract user-defined variables with pass-through application data and the score data from the quiz to be loaded into a SQL database; however, that file is no longer being generated (or named) correctly and parsing fails.

I am using Captivate 7 and 8 files (published for SWF and HTML5) on a Windows 7 platform connected to a SQL Server 2012 server - the application that calls the Captivate files is an ASP front end with C# backside. Chrome (current version is 54) is our preferred browser for our application but I do use IE when necessary. Not sure if this is a Captivate issue, browser issue, server issue, network issue, or subset combination of each - but at a loss as to where to investigate next.

Even when I attempt the 'Preview' within Captivate, I get the same "Unknown Error" - this is why I'm suspecting that our server (or even Network) is not returning the proper response to Captivate to indicate a successful connection to the internal server for posting. Note: Supplying a bad URL for the internal server in Captivate does generate a "Wrong URL" error in the Status Message window when posting.

Any ideas? Thanks.