It may have something to do with the WIIScrubber version that you're using.
WIIScrubber 1.21 does work with the PAL version of Mario Kart Wii, but I'm not too sure about the NTSC version. However, the NSMB Wii ISO doesn't work at all with WIIScrubber 1.21, but it does work with WIIScrubber 1.4.
Also, make sure that your ISO isn't a read-only file, since WIIScrubber refuses to load read-only ISOs.
No

Im using wiiscruber 1.21 but it says io_seek