Interesting. The NAND backup thing is a bug in bootmii beta version 3.
System menu v0
I wonder what these value are on a working Wii, not having preloader myself. Edit: Checked youtube and for 3.4 it should say IOS50 System Menu v384, v385 or v386
Whatever you did to install systemmenu v386 didn't work...or...your sys conf is corrupt and pointing to a null value.
I recommend installing v386 again, I'm assuming you are 3.4PAL. If you can't load boot.dol with preloader you can use cboot2 to load boot.dol as described in the thread below.
If that fails then you should look into your sys conf. There was a thread on here a little while back where a guy had a corrupted sys conf file that was fixed quite simply in the end. Have a good read through this thread and in particular this page which has a solution http://www.wiihacks.com/bricked-wii-...eogamma-4.html -- I don't think this is the case but could be wrong--
I have no idea why preloader works as it is not functional on IOS50. Maybe you have IOS60 installed or something from the tutorial.