Actually, TTS is an audio/video format and if you have applications related to audio/video, then the file will be associated as being a multimedia one. The easiest way to fix this error is by resetting the file association. Go to the installation folder of Typing Time and locate the TTS file. Right click it and select Open with. Choose Typing Time if it's in the list, otherwise use the Browse button to locate the main executable. Select it then tick the option on the same window to always open this type of file with the Typing Time app. It should work this way.