There is a simple protection on this, through all loaders, and i've read multiple replies in this very post telling what the protection is and the only current way to get it to work. Why dont people just take 10 mins to read the whole thread, instead of reading the first post and then replying for help. Rare.
Anyhow .. this game simply checks your IOS53, if it as any patches (trucha, etc..) it wont work. To get the game to work, just use Dop-mii and select IOS53 to install and when it asks if you want apply each patch, just select 'no'. The game WILL work then.
Unfortunately, a few games need to have IOS53 patched to work (NSMBW, Some wiiware games, etc). So, the only way to play all games, currently, is to reinstall IOS53 (unpatched) before playing RL3, then reinstall IOS53 (with patches) after finished.
NOTE: You can play NSMBW by using a patched copy, I think, and some ppl may not play any of the other titles that need a patched IOS53, so just installing a clean, unpatched IOS53 Will suffice for them permanently, only yourself can really know if you need the IOS patched or not. Give it a go, and see if any of the other titles you play need to have 53 with patches applied. Either way, if you wanna play RL3 you need an unpatched IOS53 (install via Dop-Mii).
For the various loaders, I was thinking if its possible to select a 'custom' IOS to start games, say IOS251 for example, we could use Dop-Mii to install an unpatched IOS53 in slot 251, thus leaving the trucha'd 53 intact for NSMBW & other titles that need it. I am no Wii prohrammer so have no idea how difficult it would be to add another 'custom' IOS slot (ie./ 251) to each loader, but imagine as most can already switch between 222,223,224,249 & 250 it wouldn't be too difficult. Or, someone could try it via disc using softchip loader, and choosing a custom IOS that is basically an unpatched 53. I do t have this on DVD-R else I would test it, Its not my type of game, I just had to post the simple fix here as each day I login, I see more replies asking how to play in full-mode.
Anyhow, thats how to unlock this game and an idea on a permanent fix, so if anyone wants to really play this, yet want their IOS53 left patched for othrr games, try the Softchip with custom 251, as detailed above ..
hope I've helped those wanting to play this in more than just demo mode .. :>