The installer is not supporter on 10.5.x, you must use instead the files for manual installation:
- Quit Ableton Live.
- Navigate to Applications/Live 8.x.x/
- Find the Ableton Live icon inside that folder and right click it or ctrl+click it.
- A drop down menu should appear, select "Show Package Contents" it is the second option starting from the top.
- A new window will pop up. Navigate to Contents/App-Resources/MIDI Remote Scripts/
- Copy the Griid folder here from the zip
- Copy the Griid Connector to your Applications folder
Now you can follow the regular instructions for connection.