How can I further troubleshoot an Internal Server Error accessing the Answers page for the QA Plugin

I have been attempting to diagnose and fix an Internal Server error which occurs whenever I attempt to access the "Answers" page of the Q&A Wordpress plugin. (on our 'intended' production site - it's not live yet).

We are hosting the Wordpress site, using IIS.

I have ascertained from the Windows Event Log on the server that the error which occurs is a Stack Overflow errors. (Error code "0x000000fd").

I have deactivated the plugin and deleted it, however when doing this I notice that the files are not removed from the file system. (On one attempt I physically deleted the files from the server before reinstalling the Q&A plug in.) I also note that even though, when you delete the plug in you receive a warning that data will be deleted, it is not being deleted, because when I reinstall the plug in, that data is all still there??

I have systematically disabled all other plug ins, and changed themes back to the default and nothing makes any difference.

After every test, the Internal Server error still occurs when I access the Answers page.

I have the plug in working on a different site and it's fine. I have ensured all plug ins are the same on both sites. Both sites use the same themes and for all intents and purposes "should" be the same - however the site that works, runs on an Azure web site, while of course the one with the problem runs on an in house Windows Server under IIS.

I've gone as far as comparing CSS and PHP files line by line for any differences and can find nothing.

I'm on the verge of moving to another plug in, because I simply cannot get this to work however I don't want to, because the site that works (a test site) has some seed questions and answers I'd like to import into the production site.

Where can I look to solve this problem?