It is not neccesarry to switch to fat32 in order to fix your problem.
In fact its the other way round. To keep your games you need to be able to access them.
As I said try wiimms wwt to fix it.
If you still want to switch to fat32 (a good idea imho) check out wbfs2fat.
It converts the FS data inplace, without needing to copy all games.
Copying all games back and forth is of course an (slow) alternative.
(If wwt says the drive is ok wbfs2fat should accept it, no mater what WBM thinks.)