According to Tom's Guide, and a number of other sources, Nintendo have confirmed that the Wii system update 4.2 is causing problems for owners of some unmodified Wii consoles.

Considering that this update provides no real benefits to anyone, I would strongly recommend avoiding it. Hopefully Nintendo will be more careful with the next system update, and add some real new functionality while they are at it.

The advice is too late for me, having only joined this forum today, but I can report no problems with the update which I allowed to be carried out as soon as I got online about a week ago.

Good to hear it went ok for you.

It seems to be quite rare, but the update doesn't seem to add anything, so I'm staying clear for the moment. Hopefully Nintendo will work out what the problem is and release a new update.