It doesn't help much towards a solution but that's not your fault. I do appreciate your relaying further information about what the techs said.
Further details from my side: I'm away from home using my Cox account information with the internet connection at a rental property. Their internet connection is provided by Time Warner Cable.
I suspect this is the "connectivity issue"? As in a domain block on TWC IP addresses even if logging into the app using a different cable provider that has the coveted licensing agreement with TCM?
What is this feud between Time Warner Cable and TCM/Turner. Why are they making life so difficult for paying subscribers. An IP block is really going the extra mile, ridiculous. I have since noticed the same type of error occurs on CNN GO, another Turner app on FireTV.
A general FireTV connectivity issue is ruled out since every other app such as HBO GO, Showtime, etc works perfectly fine no matter what IP address I happen to be using when I connect with my properly WatchTCM licensed Cox account.
I have since tried to use my phone's hotspot connection which is an AT&T mobile IP with the same error occurring.
I logged out of the WatchTCM app, cleared data, cleared cache, uninstalled the WatchTCM app. Switched the FireTV to use the AT&T hotspot connection, re downloaded the WatchTCM app and went through the verification code process again on tcm.com/activate all on the AT&T IP. I run the app, try to play any movie and "An error has occurred" just like before. The FireTV is on the latest version of software 220.127.116.11(537175520) the WatchTCM app is the latest currently offered in the Amazon app store TCM 1.0.20160412
Are AT&T IPs also blocked? Is there a way to get a more verbose error message than "An error has occurred" so the actual problem can at least be identified?
What internet provider are you using? Does it happen to be Time Warner Cable?