Finally got it working. Here's all the steps...
- Uninstall Halo: MCC
- Shutdown (press and hold Xbox button on console)
- Power-up
- Install Halo: MCC from disc (didn't bother logging in to Live first)
...
- Uninstall Halo: MCC
- Shutdown (press and hold Xbox button on console)
- Power-up
- Install Halo: MCC from disc (didn't bother logging in to Live first)
...