Ok so I was at the consoletech guy's shop today. We tried various things, including updating the D2pro's firmware and even swapping it with a Drivekey. Still I get the Error #002.
A friend of mine BTW, has also a D2pro modchipped wii and yesterday I gave a copy of WSR for him to test it out. He said the game didn't run until after updating his Wii via Nintendo to 4.1E. That's right, he updated through Nintendo and has no problems with older and/or newer backups! He doesn't have HBC and he doesn't know a thing about softmodding. He doesn't care about VC/Wiiware so he has no custom cIOS no nothing. His wii is pretty much unmodified except the D2pro.
I'm totally confused now. His modchip should've been rendered useless says the console tech. But I saw with my own eyes that he's able to run any backup fine.
The last thing I have in mind is updating my Wii (which was updated through this guide with every other thing including trucha bug restorers cIOS etc.) via Nintendo since last day when I went to the settings menu to test the internet connection "an update is available" or something like that came up to the screen even though I'm at 4.1E, and I canceled it.
So I'm gonna try it this evening. And IF ALL ELSE FAILS MISERABLY I'm considering grabbing my friend's unmodified Wii, installing Bootmii to it, backing up his NAND and copying it to myself...