This error always refers to the TT.int file. It means TT.int is missing or corrupted.
To fix the error, copy TT.int from a PC with a working install of the same TinyTERM version. If one is not available, uninstall TinyTERM and delete the C:\Program Files\Century directory. Then reboot the PC and reinstall TinyTERM. Once the error is corrected, back up TT.int so you have a replacement copy if the error happens again.
A common cause of TT.int corruption is antivirus software. It’s just a collection of messages, but sometimes it gets incorrectly flagged as a virus and quarantined. Where possible, exempt TT.int from your virus scanner to prevent that.