I have a similar issue on a mates Wii.
Tried to install today World of Goo, and Pokemon Rumble. (and update Priiloader from 0.2 or 0.3 to 0.4)
Its a otherwise Stock 4.2E Wii, updated by Ninti, then Hacked by the CSG.
Updated Priiloader 1st, then rebooted, all good.
The proceeded to use MMM to install the 2 x WADS.
Received NO errors.
Rebooted to System Menu, immediatly get a Memory Full error, and thrown to the Data Management screen?
Sure enough, 0 blocks free. Whassup?
Remove both the newly installed WADs freed up around 350 blocks. Mine at home whcih is very similar, has over 1000 blocks free??
Have to ring him tomorrow and confirm if he has the Internet Help channel, which I doubt when I was looking at the installed channels and saves.
Any other soutions, could it be caused by Priiloader. I never checked how many were free prior to twiddling today??
I also removed Priiloader, same free blocks??
Could I have corruption?, is their any utility to show the NAND memory usage by channel/savegame?
We do have a NAND backup, but only bootmi as IOS (New unit)