Aha! I fixed my problem:
Well, this particular Wii was purchased on Ebay. It came with 3.1U, and I immediately bannerbombed, bootmii boot2'ed and backed up that Nand awhile back. I performed a method of upgrading/softmodding using an old guide and eventually moved up to v4.1U. All worked fine...
But, I wanted to find a truly offline upgrade method, and this guide seemed to be the ticket. But, when I performed the upgrade, games would not play (or would have black screen on exit). So, this is what I did:
I installed *just* cIOSrev10 on the 3.1U system. Same deal, games not loading/blacking out. I figured this was odd.
I removed the HBC from the 3.1U nand and formatted the system. Instant brick. Lucky for boot2 bootmii
I restored to the 3.1U nand AGAIN, removed the HBC, and this time did the Nintendo update. Then I formatted. THis worked, and brought me right back to initial setup on reboot. Now I made a backup of THIS nand.
Followed the offline guide again and it works perfectly.
Bottom line is that the previous owner did *something* to the console...not exactly sure. The upgrade then format apparently wiped it clean again and now it works. Wow...what a fiasco, but at least I know what needs to be done should I ever upgrade somebody elses system.
Final word:
This offline guide is quite possibly the best/quickest/easiest guide to follow on the net. I literally had the system running in a matter of minutes. Surely a milestone quicker than my old previous online method.
Great job!