That's because your SCART is awaiting RGB signals but NTSC video mode on Wii outputs S-Video instead of RGB. This was a common issue with early homebrew on PAL Wii when using SCART (no problem when using the composite cable).
The mod probably setups the wrong video mode for 240p (and 480i apparently), it should be NTSC for NTSC consoles and EURGB60 for PAL consoles.
Excellent comment Jacobeian, thank you very much.
Please libertyernie, can something be done about this issue. Currently is not possible for europeans to get 240p mode.