You didnt mention your Roku model # or firmware version (Settings/System/About) or app version (highlight the app and press Options (*) on the remote).
You can try reinstalling the TCM app:
1) Remove the TCM app (Highlight the app, press the Options (*) button on the remote, then Remove)
2) RESTART the Roku (Settings/System/System restart/Restart) <-- MUST DO THIS HERE!!!
3) Re-install the TCM app
(If you dont restart after removal, settings/cached data associated with the app are left behind and it wont be a clean re-install)
However, reinstalling isnt working for many users, especially those with older models:
Make sure you report the TCM app not loading to Roku:
Highlight Watch TCM,/Options (*)/Give us Feedback/Channel failed to launch
And to TCM: