Maybe you can try different cIOS'es to load the game. In stead of 249, try 222 or 223. It's in the options menu of the USB loader. And maybe it will help if you load the ISO onto the HDD and then play them.
And updating or changing the IOS of the Wii is a bad idea. It can totally brick your Wii since the version of the IOS is firmware dependent.
If it's possible you should stay on firmware 4.1. 4.2 is just bullcrap from nintendo to block HBC and stuff.